Main Ideas and Themes

### Passage
The Sunless Abyss: How Deep-Sea Hydrothermal Vents Redefined the Boundaries of Life

For centuries, a fundamental tenet of biology was that the Sun served as the ultimate source of energy for all life on Earth. Through the process of photosynthesis, plants, algae, and cyanobacteria capture solar radiation and convert it into chemical energy, forming the indispensable foundation of global food webs. In ecosystems ranging from tropical rainforests to the open ocean’s photic zone, life was understood to be completely dependent on the penetration of sunlight. Even in the ocean’s twilight zones, organisms relied on the biological pump—a continuous drift of organic debris, colloquially known as "marine snow," falling from the sunlit waters above. It was widely accepted that without sunlight, complex ecological systems could not exist.

This biological dogma was shattered in 1977 during an expedition by the research submersible *Alvin* to the Galapagos Rift, a volcanic ridge in the eastern Pacific Ocean. Geologists searching for underwater hot springs discovered thriving communities of giant red-tipped tubeworms, large clams, and blind crabs clustered around hydrothermal vents nearly 2,500 meters below the surface. In this benthic realm of perpetual darkness, freezing temperatures, and crushing pressures, scientists did not find a sparse wasteland scavenging on scarce crumbs from above. Instead, they encountered a dense biomass that rivaled the productivity of coral reefs.

The existence of these vibrant deep-sea communities presented an immediate paradox: how could such an abundant array of complex life thrive in the complete absence of solar energy? The answer lay in a biological process previously considered minor and ecologically insignificant: chemosynthesis. Unlike photosynthesis, which uses light to synthesize organic compounds from carbon dioxide and water, chemosynthesis relies on the oxidation of inorganic molecules to produce energy. At hydrothermal vents, superheated water enriched with dissolved minerals spews from Earth’s crust. Among these minerals, hydrogen sulfide ($H_2S$)—a chemical highly toxic to most terrestrial and shallow-water organisms—serves as the primary energy currency.

Specialized, unicellular organisms known as chemolithoautotrophic bacteria are the engines of these ecosystems. These microbes oxidize hydrogen sulfide, utilizing the energy released from this chemical reaction to convert carbon dioxide into organic molecules. In doing so, these chemosynthetic bacteria serve as the primary producers of the vent communities, occupying the ecological niche filled by plants on land. Some bacteria form thick, mat-like colonies on rocky surfaces near the vents, which are grazed upon by small snails, limpets, and shrimp. Others have evolved highly specialized symbiotic relationships with larger organisms, most notably the giant tubeworm *Riftia pachyptila*.

The symbiotic relationship between *Riftia pachyptila* and chemosynthetic bacteria is one of the most remarkable evolutionary adaptations in the natural world. These tubeworms, which can grow up to eight feet in length, possess neither a mouth, a gut, nor an anus. Instead, their internal cavity is filled with a highly vascularized organ called a trophosome, which houses billions of symbiotic bacteria. The tubeworm's bright red plumes absorb dissolved oxygen, carbon dioxide, and hydrogen sulfide directly from the hydrothermal fluids and transport them via specialized hemoglobin to the trophosome. The bacteria oxidize the sulfide to produce organic carbon, which nourishes the host tubeworm, while the tubeworm provides the bacteria with a steady supply of reactants and a safe habitat.

Ultimately, the discovery of hydrothermal vent communities permanently transformed our understanding of life by demonstrating that complex, highly productive ecosystems can exist entirely independent of solar energy through the process of chemosynthesis. This paradigm shift has had profound implications extending far beyond marine biology. Astrobiologists, for instance, have revised their criteria for search zones of extraterrestrial life. Rather than limiting their search to planets with sunlit surfaces, they now look to icy moons within our solar system, such as Jupiter’s Europa or Saturn’s Enceladus, which are believed to possess sub-surface liquid oceans heated by tidal forces and volcanic activity, potentially hosting hydrothermal systems of their own. Furthermore, evolutionary biologists hypothesize that hydrothermal vents, with their rich chemical gradients and protected deep-sea environments, may have served as the cradle for the origin of life on Earth itself.

***

Based on the passage, is the following statement true or false?

"The discovery of deep-sea hydrothermal vent communities permanently transformed biological science by demonstrating that complex, highly productive ecosystems can exist entirely independent of solar energy."

The following paragraphs are from a natural science essay about deep-sea ecosystems:

[Paragraph 1] In 1977, researchers aboard the research submersible Alvin made a discovery that transformed biology. Deep on the ocean floor near the Galápagos Rift, they found hydrothermal vents spewing superheated, mineral-rich water. Surrounding these vents were thriving communities of giant tube worms, clams, and crabs, existing in complete darkness. This finding shattered the long-held scientific consensus that all biological communities on Earth require sunlight as their primary source of energy.

[Paragraph 2] At the heart of this dark ecosystem are specialized bacteria that have bypassed the need for solar radiation entirely. Rather than relying on photosynthesis, these microbes perform chemosynthesis. They metabolize hydrogen sulfide—a compound toxic to most land-based organisms—flowing from the vents and convert it into organic matter. This process forms the base of the food web, nourishing the larger animals that live clustered around the vent openings.

[Paragraph 3] The realization that life can flourish in such extreme, sunless environments has profound implications for astrobiology. Scientists now look to the icy moons of the outer solar system, such as Jupiter's Europa and Saturn's Enceladus, with renewed optimism. If liquid oceans exist beneath their frozen crusts, heated by tidal forces, hydrothermal vent communities could theoretically survive there, completely isolated from any star's light.

Match each paragraph from the passage to its primary paragraph-level main idea.

The following paragraph is from an essay about nineteenth-century urban planning:

During the late nineteenth century, the growth of municipal sewage systems in European cities did more than just improve public health; it radically transformed urban geography. Prior to these subterranean networks, waste disposal was localized, often relying on cesspools or night-soil collectors whose routes dictated the physical layout of neighborhoods and restricted expansion. The installation of unified underground drainage pipes allowed cities to grow outward without the constant constraint of proximity to waste disposal sites. Consequently, previously uninhabitable lowlands were reclaimed for housing, and the spatial division between affluent and working-class districts began to shift as municipal infrastructure standardized living conditions across municipal boundaries.

Which of the following best states the main idea of this paragraph?

Although standard histories of astronomy often credit Nicolaus Copernicus with single-handedly initiating the heliocentric revolution, a closer examination of his landmark 1543 treatise, De revolutionibus orbium coelestium, reveals a far more conservative thinker bound to ancient traditions. Copernicus indeed placed the Sun at the center of the universe, but he did so not to chart a path toward modern physics, but rather to salvage the classical Greek ideal of uniform circular motion. Frustrated by the Ptolemaic system's reliance on the equant—an imaginary point from which a planet's speed appeared uniform, even though its actual speed along its orbit varied—Copernicus sought a geometrically 'pure' alternative. To maintain perfect circular orbits without the equant, he was forced to introduce a complex web of epicycles and eccentrics, ultimately creating a system nearly as cumbersome as the one he sought to replace. Furthermore, Copernicus retained the Aristotelian belief in solid crystalline spheres carrying the planets, and he remained convinced that the universe was finite and bounded by a sphere of fixed stars. It was not Copernicus, but later figures like Johannes Kepler��who abandoned circular orbits for ellipses—and Galileo Galilei—who dismantled the crystalline spheres—who truly forged the conceptual tools of modern astronomy. Copernicus’s work was less a modern breakthrough than a final, sophisticated attempt to perfect classical geometry.

Based on the passage, which of the following statements best expresses the main idea of the author's analysis of Copernicus?

The following paragraph is excerpted from an essay about historical printing techniques:

[1] Although the invention of the printing press is widely credited to Johannes Gutenberg in fifteenth-century Europe, movable type technology actually originated in East Asia centuries earlier. Bi Sheng developed ceramic movable type in China around 1040, and by the thirteenth century, Korean artisans had advanced this process by using metal type to print documents. While Gutenberg's press revolutionized European literacy, it built upon technological foundations laid down by Asian inventors who had already recognized the efficiency of reusable, individual character pieces.

Based on Paragraph 1 (lines 1–7), which of the following statements best expresses the paragraph's main idea?

For decades, historians of science have debated the primary catalyst of the Scientific Revolution. Standard narratives often privilege the mathematical breakthroughs of Copernicus and Galileo, arguing that the quantification of nature was the singular engine of modern empirical inquiry. However, this perspective overlooks the profound influence of early modern craftsmanship. It was not the abstract theorists alone, but rather the translation of tacit, workshop-based knowledge into formal written treatises that bridged the gap between speculative philosophy and experimental science. Guild artisans, who long worked with glass, metals, and pigments, had developed rigorous, non-verbal methodologies for testing material properties and refining mechanical processes. When scholars like Francis Bacon began to codify these practical techniques, they did not invent the empirical method; they merely academicized a system of physical verification that had existed in workshops for generations. Thus, while the mathematical equations of astronomers provided the language of the new science, the physical practice of validation was inherited directly from the vernacular labor of artisans, making the workshop the true crucible of the scientific method.

Based on the passage, which statement best summarizes the author's primary argument?

While many avian species exhibit basic problem-solving abilities, the New Caledonian crow stands out for its sophisticated tool manufacture and usage. In the wild, these crows do not simply search for pre-existing objects to use as tools; rather, they deliberately construct them from raw materials. For instance, they fashion hooks from thin, barbed twigs to extract wood-boring larvae from deep tree crevices. They also shape tools from the stiff, serrated leaves of the pandanus plant, cutting them into precise tapered strips. Laboratory observations confirm that these birds can even bend wire into hooks to retrieve food baskets from vertical tubes. While some researchers once believed that these crows merely copied simple behaviors from their parents, extensive field studies have shown that young crows undergo a prolonged learning period to master the complex geometry of leaf-tool construction. This remarkable behavior demonstrates a level of cognitive complexity previously associated almost exclusively with primates, suggesting that complex tool manufacture and use can evolve independently in species outside the mammalian lineage.

Which statement best summarizes the primary argument presented in the passage?

Cartography has long been viewed as a mirror of
geographic reality, a neutral science dedicated to
representing the physical contours of our world with
increasing precision. Historically, maps served practical
5 ends—navigation, boundary definition, and resource
planning. The introduction of standardized grid systems
and coordinate networks further solidified the public
perception of maps as objective documents, free from
ideological influence.
10 However, this veneer of objectivity often obscures
the cartographer’s role as an active editor of space.
The act of mapmaking is fundamentally an exercise in
selection, simplification, and omission. To fit a
three-dimensional sphere onto a two-dimensional plane,
15 choices must be made; certain landmarks are elevated to
prominence, while others are erased entirely. Far from
being passive records of geography, maps are highly
constructed arguments that project the values, priorities,
and territorial claims of their creators. Every choice of
20 projection, symbol, and border placement functions as a
rhetorical device, subtly shaping the viewer's spatial
understanding to align with specific political or cultural
perspectives.
Consequently, modern critical cartography urges
25 readers to deconstruct these spatial representations,
looking beyond the physical details to decode the
underlying power dynamics. By examining what is left
off a map, scholars can reveal the silent exclusions
that marginalized certain populations during imperialist
30 expansions. In this light, maps are no longer seen
merely as tools for navigation, but as historical texts.

Which of the following statements best expresses the main idea of the second paragraph (lines 10–23)?

Ancient Greek theatres, such as the one at Epidaurus, are renowned for their extraordinary acoustics, which allow spectators in the highest rows to hear actors clearly without amplification. For decades, popular consensus attributed this phenomenon to the shape of the theatre's seating tiers, which acts as a natural sound filter. A recent study, however, challenges this singular explanation by analyzing the physical properties of the materials used in construction. Researchers discovered that the highly porous limestone of the benches plays a far more critical role than previously understood. This limestone structure acts as a natural sound trap, absorbing low-frequency background noises—such as the rustle of leaves or the murmur of the audience—while reflecting the high-frequency voices of the actors back toward the seating area. While the curvature of the amphitheater certainly helps direct sound waves, it is the selective filtering by the limestone material that prevents the actors' voices from being drowned out by ambient noise. Thus, the acoustic clarity is a result of a sophisticated interaction between geometry and material science, rather than spatial design alone.

Which of the following statements best summarizes the main idea of the passage?

In the late nineteenth century, ethnologists began deploying the newly invented wax cylinder phonograph to document Native American musical traditions. Scholars like Alice Fletcher argued that the technology offered an objective record, capturing acoustic nuances that Western musical notation—with its reliance on diatonic scales—could not represent. By capturing pitch fluctuations, microtonal inflections, and rhythmic irregularities, the phonograph supposedly bypassed the subjective biases of the transcriber. However, this technological optimism overlooked the medium's inherent limitations. The wax cylinders' restricted frequency response and high surface noise often obscured the very subtle vocal textures the ethnologists sought to preserve. Furthermore, the physical constraints of the cylinder—which could record only about two to three minutes of audio—forced performers to truncate longer ceremonial pieces, altering the natural structure of the music. Consequently, while the phonograph was celebrated as a neutral vessel for raw data, its technical parameters actively shaped, and in some cases distorted, the cultural expressions it was meant to passively preserve.

Which of the following statements best summarizes the main idea of the passage?

Below is an excerpt from a Humanities passage discussing the history of cartography:

While it is tempting to view the elaborate sea monsters and mythological beasts adorning early modern maps as mere whimsical decoration or a naive surrender to superstition, these illustrations served a more rigorous cognitive function. In cartography’s transitional era, blank spaces on a map were not merely neutral voids; they represented existential anxiety and destabilized the authority of the mapmaker. By populating these terrae incognitae with standardized chimeras, cartographers did not simply fill space; they categorized the boundaries of human knowledge. The monsters were visual placeholders for specific categories of environmental hazards—such as unpredictable currents, shoals, or magnetic anomalies—translated into a symbolic language familiar to contemporary mariners. Thus, what modern eyes dismiss as flights of fancy was, in fact, an early, structured attempt to systematize the unknown, establishing a taxonomy of expectation that transformed terrifying uncertainty into readable, navigationally useful signs.

Which of the following statements best summarizes the main idea of this paragraph (lines 28–46)?

For centuries, the camera obscura had been used by artists as a tool for tracing landscapes and portraits, yet it lacked the ability to permanently record the projected images. This limitation sparked a race among nineteenth-century inventors to capture light on a physical medium. The first breakthrough came in 1826 when Nicéphore Niépce used a bitumen-coated pewter plate to capture a faint, highly contrasted view from his window, requiring an exposure of over eight hours. Soon after, Louis Daguerre refined this process by introducing silver-plated copper sheets sensitized with iodine vapor, which cut exposure times to under thirty minutes and yielded remarkably sharp details. While Daguerre’s 'daguerreotype' gained immense popularity, it had a crucial drawback: each plate was a unique, non-reproducible image. It was ultimately William Henry Fox Talbot's development of the calotype process—which used paper negatives to print multiple positive copies—that laid the foundation for modern photography. Although Talbot's early images lacked the clarity of Daguerre's, the capacity for mass replication transformed photography from a singular curiosity into a powerful, democratic medium of communication.

Based on the passage, which statement best summarizes the author's primary claim about the evolution of early photography?

The following passage is adapted from an article about deep-sea oceanography.

Paragraph 1 (lines 1-10)
In 1977, oceanographers aboard the research vessel Alvin made a baffling discovery along the Galapagos Rift, thousands of meters below the ocean surface. Expecting to find a biological desert due to the complete absence of sunlight and near-freezing temperatures, scientists were instead confronted with a thriving, dense community of previously unknown organisms, including giant tube worms and ghost-like crabs. This startling find shattered the long-held scientific assumption that all complex marine life ultimately depends on solar energy filtered down from the upper layers of the ocean.

Paragraph 2 (lines 11-19)
At the heart of this deep-sea ecosystem lay hydrothermal vents—geological fissures that spew superheated, mineral-rich water from beneath the Earth's crust. As this fluid mixes with the cold seawater, minerals precipitate out, forming chimney-like structures. Oceanographers quickly realized that these vents act as vital heat and chemical conduits, transferring thermal energy from the planet’s mantle into the ocean depths, thereby maintaining localized temperatures that can support life.

Paragraph 3 (lines 20-29)
Subsequent microbiological analysis revealed that the biological engine driving this ecosystem was not photosynthesis, but chemosynthesis. Specialized bacteria, dwelling inside the tissues of the tube worms or forming mats on surrounding rocks, oxidize toxic hydrogen sulfide escaping from the vents. By converting these chemical compounds into organic matter, these microbes form the foundational base of the local food web, proving that life can flourish entirely independent of sunlight.

Match each paragraph from the passage to its primary paragraph-level main idea.

While cuneiform is celebrated today as the world’s first true writing system, its origins were far from literary. Developed by the Sumerians around 3200 BCE, the earliest cuneiform tablets were strictly utilitarian, serving as ledger sheets to record agricultural surpluses, temple inventories, and beer rations. These initial clay tablets utilized pictographs to represent physical goods, which functioned effectively for basic economic transactions. However, as Sumerian city-states grew in population and complexity, a bureaucratic class emerged that required a more flexible method of communication. Over centuries, the script evolved from simple pictographic representations to a highly sophisticated phonetic system capable of expressing abstract concepts. This transition was not merely a technical refinement; it marked a profound cognitive shift in how humanity recorded history and organized society. With phonetic cuneiform, scribes could transcribe spoken language, leading to the preservation of legal codes, diplomatic correspondence, and epic poetry such as the Epic of Gilgamesh. Ultimately, cuneiform's evolution from a simple administrative accounting tool to a complex linguistic system enabled the consolidation of state power and the birth of written culture, transforming clay from a temporary ledger into a permanent repository of human thought.

Which statement best summarizes the author's primary argument regarding the evolution of cuneiform?

The following paragraphs are from a natural science passage discussing beaver dams:

[Paragraph 1]
Beavers are well-known for building wooden dams across streams and small rivers. By piling branches, logs, stones, and mud, they block the natural flow of water, which forces it to pool upstream. This construction process transforms a quick-moving stream into a deep, quiet pond that serves as a safe home for the beaver family.

[Paragraph 2]
In addition to providing shelter, these beaver ponds act as natural filtration systems. As the blocked water slows down, suspended dirt, sand, and organic debris sink to the bottom of the pond rather than floating downstream. This trapping of sediment helps clean the water, reducing the accumulation of silt in larger reservoirs and lakes further down the river system.

[Paragraph 3]
Furthermore, the quiet water and surrounding wetlands created by the dams attract many other species. Algae and aquatic plants thrive in the still ponds, providing food for insects, fish, and amphibians. In turn, these creatures draw waterfowl, birds of prey, and mammals, making beaver ponds hotspots of biological diversity.

Match each paragraph from the passage to its primary paragraph-level main idea.

The following passage is adapted from an essay exploring the evolution of sound accompaniment in early silent cinema.

[Paragraph 1]
While modern audiences associate the 'silent' era of film with quiet contemplation or simple piano melodies, the early nickelodeons of the 1900s were sites of acoustic chaos. Showmen deployed a haphazard array of player pianos, drums, and live sound effects to drown out the whirring of the projector and the chatter of the crowd. Rather than enhancing the narrative, this initial acoustic landscape was fragmented and local. Musicians, lacking cue sheets, frequently chose songs that clashed with the screen action—playing upbeat ragtime during tragic scenes—which critics condemned as a vulgar distraction that fractured the spectator's immersion.

[Paragraph 2]
By the 1910s, however, film distributors recognized that unstructured noise threatened the medium's narrative authority. The industry responded by standardizing accompaniment through the distribution of official 'cue sheets' and compiled photoplay music libraries. This shift transformed cinema music from a chaotic, localized performance into a disciplined rhetorical tool. By aligning specific musical motifs with character actions and emotional arcs, the standardized score began to function as an implicit narrator, guiding the audience's psychological state and clarifying complex plot points without the need for excessive intertitles.

[Paragraph 3]
Yet, the introduction of live sound effect devices—such as machines mimicking wind, thunder, or galloping horses—introduced a distinct aesthetic tension. Unlike music, which operated metaphorically, sound effects aimed for literal representation. When synchronized poorly, these mechanical sound effects shattered the illusion of reality, drawing attention to the artificiality of the theatrical space. Film theorists of the era argued that while music elevated the film's poetic reality, literal sound effects often anchored the film too rigidly in the mundane, disrupting the delicate boundary between cinematic illusion and physical reality.

[Paragraph 4]
The arrival of synchronized sound-on-film technology in the late 1920s did not merely automate accompaniment; it fundamentally redefined the relationship between the exhibition space and the filmic text. With the soundtrack permanently printed alongside the visual frames, the studio wrested control of the acoustic experience from local exhibitors and live musicians. This technological consolidation eliminated the variability of live performance, replacing a highly localized, interactive public event with a closed, standardized, and unalterable aesthetic object.

Which of the following pairings correctly matches each paragraph to its primary paragraph-level main idea?

The passage is as follows:

In the mid-eighteenth century, the publication of Samuel Johnson’s *Dictionary of the English Language* was heralded as a monumental attempt to stabilize a tongue perceived as drifting toward chaotic degeneration. Popular historiography often characterizes Johnson’s project as a conservative effort to arrest linguistic mutability, freeze vocabulary, and establish immutable standards of correctness. Indeed, Johnson’s early writings, particularly his 1747 *Plan of a Dictionary*, suggest an ambition to 'embalm his language, and secure it from corruption.' However, this initial impulse represents only the catalyst, not the ultimate reality of the project. As Johnson progressed through the compiling of usage, his philosophy underwent a profound shift. By the time the dictionary was published in 1755, Johnson openly acknowledged that language is a living organism, constantly reshaped by the daily transactions of its speakers. The true significance of his work lay not in an impossible arrest of language change, but in how it negotiated the socio-economic anxieties of the rising middle class. By systematically cataloging words alongside literary citations, the *Dictionary* provided a map of social mobility, offering the burgeoning bourgeoisie a manual for acquiring the cultural capital of the aristocracy. Thus, while the dictionary did document spelling and definition, its primary cultural function was to construct a class-conscious linguistic standard that reconciled the inevitability of change with the societal demand for elite distinctiveness.

Which of the following statements best summarizes the main idea of the passage?

The following passage is adapted from an essay discussing the development of modern architectural acoustics.

Paragraph 1 (lines 1–12)
Historically, the design of public speaking and performance spaces was a matter of trial, error, and structural replication. Builders relying on classical proportions did not understand why some halls resonated beautifully while others swallowed sound. It was not until 1895, when Harvard University tasked a young physics assistant professor named Wallace Sabine with correcting the abysmal acoustics of the newly constructed Fogg Art Museum lecture room, that the field of architectural acoustics began to transition from a mystical craft into a quantifiable science. Sabine began a series of meticulous late-night experiments, moving seat cushions and rugs in and out of the empty lecture hall, timing how long a standard sound took to decay to inaudibility.

Paragraph 2 (lines 13–24)
By systematically altering the room's materials, Sabine defined the mathematical relationship between a room's volume, the total sound-absorbing quality of its surfaces, and its reverberation time. This discovery provided the first reliable metric for acoustic design. Rather than relying on traditional forms or visual symmetry, architects could finally calculate sound behavior before construction began. Sabine's work proved that acoustic quality was not a product of luck or architectural aesthetics, but a predictable physical phenomenon that could be controlled through the deliberate choice of materials.

Based on the passage, which of the following statements best expresses the primary point of Paragraph 2 (lines 13���24)?

For decades, ecological studies of forest canopies were severely limited by accessibility, forcing researchers to rely on indirect observations from the forest floor or hazardous climbing techniques. This changed dramatically in 1990 with the installation of the first forest canopy crane in a temperate forest in Washington State. By adapting construction cranes for scientific use, researchers gained unprecedented, non-destructive access to the three-dimensional space of the treetop canopy. These cranes allow scientists to suspend themselves in gondolas, moving smoothly throughout the foliage to measure photosynthesis, insect diversity, and gas exchange in situ.

While canopy cranes are expensive to install and maintain, their contribution to understanding forest ecosystems is immense. For instance, studies conducted via crane have revealed that the canopy houses up to half of all terrestrial biodiversity, much of it previously undescribed. Additionally, measurements taken from crane gondolas have refined global carbon-cycle models by showing that mature forest canopies absorb significantly more carbon dioxide than previously estimated. Ultimately, the canopy crane has transformed forest ecology from a science of estimation to one of direct, precise measurement, reshaping our comprehension of global climate dynamics.

Which of the following statements best summarizes the main idea of the passage?

The passage below is adapted from an article about the history of standardized timekeeping.

Paragraph 1 (lines 1-8):
Historically, every town kept its own local time based on the sun's position, leading to hundreds of local times across a single country. This system worked fine when travel was slow, but the rapid expansion of railroads in the mid-nineteenth century created scheduling chaos. Trains moving between cities faced conflicting arrival and departure times at every station. A single uniform standard was desperately needed to prevent train collisions and coordinate travel schedules.

Paragraph 2 (lines 9-16):
In response to this confusion, Sir Sandford Fleming proposed a system of twenty-four standard time zones, each spaced fifteen degrees of longitude apart. Fleming suggested that the entire world be divided into these zones, with all clocks within a single zone synchronized to the same hour. His proposal was initially adopted by major railway companies, who implemented four standard time zones in North America to organize their routes.

Paragraph 3 (lines 17-24):
To make this regional system global, representatives from twenty-five nations gathered at the International Meridian Conference in Washington, D.C., in 1884. The delegates selected Greenwich, England, as the prime meridian, establishing it as the zero-degree point of longitude. This decision allowed the creation of a unified global time system, anchoring the world’s twenty-four time zones to a single, universally recognized starting point.

Match each paragraph of the passage with its primary main idea.