Reading Comprehension: Detail and Inference

Read the following sentence from an academic paper on evolutionary paleontology:

"While early twentieth-century paleontologists maintained that the rapid diversification of Devonian tetrapods was primarily driven by aquatic habitat desiccation during prolonged droughts, recent isotope analyses of fossilized tooth enamel indicate that these early tetrapods inhabited permanently inundated estuarine environments, though their structural limb modifications evolved prior to any permanent shift onto dry land."

Based on the sentence above, which of the following can be logically inferred regarding the structural limb modifications of Devonian tetrapods?

Passage:
In traditional single-sided product markets, antitrust regulators assess predatory pricing primarily by determining whether a firm sells goods below marginal cost to eliminate competitors. However, two-sided platform markets—such as digital payment networks and ride-sharing platforms—challenge this conventional framework. In these markets, platforms serve two distinct user groups whose demands are interdependent via indirect network effects; the value of the platform to users on one side increases as the number of users on the other side grows. Consequently, platform operators frequently adopt asymmetrical pricing strategies, heavily subsidizing or offering free services to one side (the "subsidy side") while extracting premium fees from the other side (the "money side") to maximize overall network participation.

Antitrust critics often misinterpret low or zero prices on the subsidy side as evidence of predatory pricing intended to drive out competing single-sided or two-sided rivals. Yet, economic analysts emphasize that such subsidization does not necessarily signal anti-competitive intent or unsustainable financial loss. Because cross-side network externalities generate substantial revenues on the money side that offset losses on the subsidy side, a price below marginal cost on one side can be profit-maximizing for the platform as a whole. Nevertheless, courts applying traditional antitrust doctrines often evaluate transactions on each side of the platform in isolation. By ignoring the financial interdependency between the two sides, judicial decisions risk misclassifying rational, output-expanding platform pricing as predatory, while simultaneously failing to recognize subtle anti-competitive foreclosures that occur when dominant platforms leverage cross-subsidization to lock in user bases across adjacent market segments.

Which of the following conclusions would an antitrust court most likely reach if it evaluates a two-sided platform's pricing structure by isolating the subsidy side without accounting for money-side revenues?

During the abrupt cooling of the Younger Dryas (circa 12,900 to 11,700 years ago), the dynamics of the southern margin of the Laurentide Ice Sheet underwent significant restructuring. Traditional glaciological models attributed the episodic accelerations of the ice sheet's ice streams predominantly to thermal insulation from thick overlying ice, which raised basal temperatures to the melting point. However, recent geochemical analysis of proglacial lake sediment cores has revealed that basal shear stress was modulated primarily by subglacial hydrological networks rather than thermal regime alone. Researchers examining trace element concentrations—specifically the ratio of manganese to calcium ($Mn/Ca$) in benthic foraminifera tests—found distinct episodic peaks corresponding to transient pulses of highly oxygenated, subglacial meltwater. These pulses coincided with periods of rapid ice-bed decoupling, during which pressurized basal water reduced effective overburden pressure. Notably, while previous hypotheses assumed that meltwater conduits maintained continuous, low-pressure drainage that stabilized the ice mass, the $Mn/Ca$ proxy evidence demonstrates that subglacial drainage operated via an inefficient, distributed network of cavities. This distributed configuration periodically trapped subglacial water under high hydrostatic pressure, thereby initiating transient ice-surging events prior to the eventual formation of channelized tunnel valleys that relieved the pressure.

According to the passage, the geochemical evidence derived from manganese-to-calcium ($Mn/Ca$) ratios in benthic foraminifera indicates which of the following regarding subglacial drainage during the Younger Dryas?

Read the following sentence from an academic study on European population genetics and historical linguistics:

"Although late twentieth-century historical linguists originally hypothesized that the structural isolation of the Basque language resulted from continuous geographic isolation in the Western Pyrenees since the Upper Paleolithic era, recent comparative genomic analyses of modern Basque populations reveal genetic signatures of significant Bronze Age steppe admixture, demonstrating that Basque speakers were not genetically isolated from neighboring Indo-European groups during the initial spread of agriculture across Western Europe."

Based on the sentence provided, which of the following statements about Basque speakers is most strongly supported?

Phytoremediation—the deployment of vegetation to decontaminate polluted soil and water—has emerged as a vital biological strategy in environmental engineering. Among hyperaccumulating flora, the ladder brake fern (*Pteris vittata*) exhibits a remarkable capacity to extract arsenic from contaminated substrates and concentrate it within its harvestable fronds. For most terrestrial vascular plants, arsenic exposure triggers immediate cellular toxicity and severe oxidative damage. In contrast, *Pteris vittata* utilizes a specialized internal detoxification pathway. Upon uptake by root transport proteins, toxic arsenate ($\text{AsO}_4^{3-}$) is swiftly reduced to arsenite ($\text{AsO}_3^{3-}$) inside root cells through the catalytic action of phosphate-induced arsenate reductase. Following this enzymatic reduction, arsenite is translocated via xylem vessels to the fern's fronds, where it is pumped across tonoplast membranes into intracellular vacuoles.

Within these vacuolar lumens, arsenite forms stable complexes with thiol-rich peptides, effectively sequestering the heavy metal away from metabolic machinery in the cytoplasm. Biochemical investigations demonstrate that phosphorus enrichment in the growth medium significantly accelerates the rate of root-to-frond arsenic translocation by upregulating phosphate-transporter gene expression. Conversely, while nitrogen supplementation increases total plant biomass, it leaves the intrinsic root-to-frond arsenic concentration ratio unchanged.

According to the passage, which of the following processes occurs within root cells of *Pteris vittata* before arsenic is translocated to the fronds?

Read the following excerpt from an academic history of nineteenth-century astrophysics:

"Although Gustav Kirchhoff’s 1859 formulation of spectral analysis enabled astronomers to identify chemical elements in the solar atmosphere, it was not until the development of gelatin-silver bromide photographic plates in the late 1870s that solar spectrographs could record spectral line shifts faint enough to verify Doppler-effect measurements of solar rotation."

True or False: Prior to the late 1870s, astronomers could identify chemical elements in the solar atmosphere using spectral analysis, but solar spectrographs lacked the sensitivity required to record line shifts subtle enough to verify Doppler-effect measurements of solar rotation.

In the landmark 1911 adjudication of Standard Oil Co. of New Jersey v. United States, the United States Supreme Court established the "rule of reason" doctrine, fundamentally reshaping federal antitrust jurisprudence under the Sherman Antitrust Act of 1890. Prior to this ruling, the judiciary adhered to a literal reading of Section 1 of the Act, which declared illegal "every contract, combination... or conspiracy in restraint of trade." Chief Justice Edward Douglass White, writing for the majority, asserted that such an inflexible construction was legally untenable, as virtually all commercial contracts restrain trade to some degree. Consequently, the Court posited that the statute prohibited only those combinations that resulted in an "undue" or "unreasonable" restraint of trade.

To determine unreasonableness, White introduced a framework centered on intent and effect: courts were required to evaluate whether a firm's conduct manifested a specific intent to monopolize or engendered consequences equivalent to monopoly power, such as artificial price escalation or output restriction. In applying this standard to Standard Oil, the Court scrutinized not merely the conglomerate's immense size, but its history of predatory pricing, rebate extraction from railroads, and exclusionary acquisitions aimed at crushing independent competitors. The Court concluded that these specific exclusionary practices demonstrated an intent to drive competitors from the market rather than achieve market leadership through superior efficiency. Thus, the dissolution of Standard Oil was ordered not on the threshold of its market share alone, but because its aggressive operational strategies breached the newly codified standard of unreasonable restraint.

According to the passage, which of the following was the direct reason the Supreme Court ordered the dissolution of Standard Oil?

In sixteenth-century Andean silver metallurgy, the transition from traditional native smelting furnaces (*huayras*) to cold-mercury amalgamation—introduced to Potosí in 1571 under Viceroy Francisco de Toledo—dramatically increased the extraction yield of low-grade argentiferous ores. However, the cold amalgamation process suffered from substantial mercury loss through the formation of insoluble calomel ($Hg_2Cl_2$) when processing ores rich in copper sulfides. To mitigate this inefficiency, metallurgist Álvaro Alonso Barba developed the hot-amalgamation or *cazo* process in the early seventeenth century. Barba's innovation involved heating crushed ore slimes with mercury, common salt, and water in copper-bottomed cauldrons rather than open patio beds.

Historians long assumed that the primary thermodynamic advantage of Barba's *cazo* technique lay solely in elevated reaction temperatures accelerating amalgamation kinetics. Recent chemical analyses of seventeenth-century slag and tailings at Tarabuco, however, demonstrate a more complex chemical mechanism. The metallic copper walls of the cauldron acted as an active reducing agent, undergoing preferential oxidation to donate electrons to ionic mercury species. This metallic copper involvement suppressed calomel precipitate formation by reducing mercurous ions back to metallic mercury before insoluble compounds could form. Furthermore, Barba’s requirement of adding concentrated brine served not merely as a chloridizing agent for silver sulfosalts, but generated copper-chloride complexes that catalyzed the reduction of silver sulfide ($Ag_2S$) without consuming elemental mercury. Consequently, while the cold patio process lost up to two kilograms of mercury per kilogram of refined silver when processing complex pyritic ores, the *cazo* method reduced mercury consumption to less than three hundred grams, rendering sub-marginal sulfide deposits economically viable.

According to the passage, the metallic copper bottom of the cauldrons used in the *cazo* process contributed to reducing mercury loss by doing which of the following?

In early eighteenth-century Britain, the extraction of tin and copper from deep subterranean mines in Cornwall was severely hampered by persistent water inundation. To mitigate this flooding, mine operators increasingly turned to Thomas Newcomen’s atmospheric steam engine, first introduced in 1712. Although Newcomen engines were thermodynamically inefficient—consuming immense quantities of coal because the main cylinder had to be alternately heated and cooled during every stroke—Cornish mine owners found their deployment economically viable due to specific local operational adjustments.

Unlike coal-rich regions such as Newcastle where fuel costs were negligible, Cornwall possessed no native coal deposits, making fuel transportation via sea extraordinarily expensive. To offset these exorbitant fuel expenditures, Cornish mining consortia introduced an integrated water-recirculation system. Under this arrangement, the engine’s primary pump lifted mine water into elevated surface reservoirs; this stored water was subsequently released to drive overshot waterwheels that powered auxiliary ore-crushing machinery. Furthermore, rather than running the engines continuously, Cornish engineers calibrated the pumping frequency strictly to coincide with local tidal influx cycles in drainage adits. This scheduled operation enabled the engines to run intermittently at maximum mechanical load, avoiding the severe efficiency losses associated with continuous low-load idling. Consequently, these tailored infrastructural practices sustained the commercial viability of Cornish mineral extraction for several decades preceding James Watt’s patenting of the separate condenser in 1769.

According to the passage, Cornish mine operators offset the high cost of transporting fuel to their mines by doing which of the following?

Passage:

In mid-nineteenth-century British industrial cities, municipal water supply networks were initially constructed by private utility companies operating under parliamentary charters. Proponents argued that private enterprise offered the capital efficiency needed to expand infrastructure rapidly. However, because private charters guaranteed monopoly rights within designated districts without capping subscriber tariffs, companies consistently prioritized high-density, affluent commercial corridors while neglecting lower-income residential perimeters. Consequently, water contamination and cholera outbreaks remained concentrated in marginalized districts throughout the 1840s.

To address these public health crises, municipal reform coalitions successfully lobbied for the Public Health Act of 1848, which authorized local boards of health to purchase private waterworks through compulsory municipalization. Surprisingly, despite acquiring the private networks, municipal boards did not immediately extend infrastructure to peripheral neighborhoods. Instead, faced with substantial debt obligations incurred from compensating former charter holders at premium valuations, these municipal boards funneled nearly all municipal revenues into servicing interest payments and maintaining existing trunk lines. Thus, counter to the expectations of reform coalitions who assumed municipalization would democratize access, the immediate financial burden of buyout compensation effectively constrained the public sector's ability to achieve broader spatial distribution of clean water until late-stage debt restructuring occurred decades later.

Based on the passage, which of the following statements regarding water infrastructure in mid-nineteenth-century British industrial cities is most strongly supported?

In the mid-nineteenth century, the papermaking industry faced a severe shortage of raw materials as rag supplies proved insufficient to meet the surging demand for printing paper. To address this deficit, inventor Benjamin Tilghman patented the sulfite process in 1867, utilizing sulfurous acid to dissolve lignin and isolate cellulose fibers from wood. Although Tilghman's initial trials demonstrated that wood pulp could yield high-quality paper, technical complications—specifically severe equipment corrosion caused by acid leakage under high pressure and temperature—forced him to abandon commercial operations.

It was not until the late 1870s that Swedish chemist Carl Daniel Ekman successfully commercialized the sulfite method by designing pressure vessels lined with lead and utilizing magnesium bisulfite instead of calcium bisulfite. Ekman's structural modification prevented vessel degradation, enabling large-scale industrial production. Simultaneously, in Germany, Mitscherlich developed a slower, lower-pressure variant of the sulfite process using indirect steam heating, which yielded longer, stronger fibers favored for heavy-duty card stock. Despite the mechanical superiority of Mitscherlich's paper, Ekman's faster, high-yield system gained rapid adoption in British and North American mills. Consequently, by the 1890s, wood-based sulfite pulp had largely superseded traditional rag stock across Western printing markets, dramatically reducing book production costs.

According to the passage, Benjamin Tilghman was unable to achieve commercial success with his sulfite process primarily because of which of the following factors?

Passage:
In analyzing the economic shocks of mid-seventeenth-century Europe, historians long attributed the widespread agricultural collapses of the 1640s primarily to localized agrarian mismanagement and protracted military conflicts such as the Thirty Years' War. However, recent interdisciplinary research combining dendroclimatology and ice-core geochemistry has forced a reevaluation of these disruptions. Dendrochronological data from subalpine conifer rings reveal unprecedented reductions in latewood density during 1641 and 1642, indicative of severe, unseasonal summer cooling. Simultaneously, polar ice cores from Greenland show distinct spikes in sulfate aerosol concentrations dating precisely to late 1640, pointing to a massive tropical volcanic eruption that injected light-reflecting sulfur compounds into the stratosphere.

While conventional historical accounts assumed that localized crop failures were exacerbated solely by army movements destroying fields, synthesizing high-resolution physical proxy records with regional grain price registers demonstrates a more complex systemic interaction. In regions entirely untouched by military activity, such as southern Scandinavia, cereal yields declined by over 40 percent in 1642, coinciding with the temperature nadir calculated from tree-ring density. Crucially, price convergence data show that shipping lanes in the Baltic Sea froze several weeks earlier than normal during the winters of 1641–1643. Although some economic historians hypothesized that regional grain market integration would normally buffer localized harvest shortfalls through maritime trade, this unexpected prolonged freezing severed key supply corridors, preventing surplus grain from reaching vulnerable urban markets. Thus, the physical evidence indicates that atmospheric phenomena initiated a cascade that crippled both agricultural output and the logistical infrastructure intended to redistribute relief supplies.

Based on the passage, evaluate whether the following statement is TRUE or FALSE:
"The physical proxy evidence presented in the passage supports the inference that the unusually early winter freezing of Baltic shipping corridors in 1641–1643 was triggered by the same atmospheric perturbation responsible for the decreased latewood density in subalpine conifers during 1641 and 1642."

Read the following sentence from an analysis of early twentieth-century oceanography:

"While early twentieth-century marine biologists hypothesized that North Atlantic cod stocks migrated along uniform thermal gradients across open waters, empirical catch logs from 1912 to 1925 revealed that localized bathymetric features, rather than sea-surface temperatures alone, governed the seasonal aggregation of spawning populations."

Based on the sentence above, determine whether the following statement is True or False:
Prior to the analysis of the 1912–1925 catch logs, marine biologists placed greater emphasis on surface thermal conditions than on seabed topography when accounting for cod migration patterns.

In plant ecology, fungal endophytes—microscopic organisms residing asymptomatically within host plant tissues—were historically characterized as strictly mutualistic partners that invariably enhance plant survival. Early field studies documented that specific endophytes produce secondary metabolites capable of deterring foliar herbivores and improving drought tolerance in agricultural grasses. However, recent investigations into Epichloë endophytes inhabiting wild alpine flora reveal a far more dynamic relationship. While these endophytes do confer drought resilience by regulating host stomatal conductance, they simultaneously consume substantial photosynthetic carbohydrates from the plant, imposing a distinct metabolic cost during periods of severe nutrient limitation.

To illustrate this metabolic trade-off, researchers measured the total reproductive output of Festuca grasses infected with Epichloë under controlled nitrogen regimes. In nitrogen-rich soil environments, infected grasses produced significantly higher seed yields than uninfected control plants; conversely, in nitrogen-depleted soils, infected grasses exhibited a fifteen percent decrease in seed biomass compared to their symbiont-free counterparts. These empirical observations demonstrate that the functional outcome of endophytic symbiosis is not static, but rather fluctuates along a conditional continuum defined by microenvironmental resource constraints. Consequently, predictive ecological models that treat fungal endophytes as universally beneficial mutualists risk miscalculating plant community adaptation under changing climatic conditions.

The author mentions the "fifteen percent decrease in seed biomass" in the second paragraph primarily in order to

Until recently, maritime historians studying fourteenth-century Hanseatic trade networks relied primarily on municipal customs ledgers to reconstruct the volume and geographic reach of timber exports from the Vistula River basin. These documentary sources suggested a sudden contraction in pine exports following the demographic disruptions of the mid-century Plague. However, recent dendrochronological analysis of ship timbers recovered from the Gdansk copper shipwreck provides a nuanced counterpoint to this orthodox narrative. Tree-ring sequences from the vessel's hull planks reveal that while timber felling in the upper Vistula catchment did drop sharply between 1350 and 1365, the vessel's framing timbers—crafted from slow-growing sessile oak harvested in the Pomeranian hinterland—exhibit continuous growth rings harvested during the precise decade of presumed economic collapse.

This discrepancy highlights a critical limitation of relying solely on municipal tax registries. Because civic ledgers recorded only commodified bulk timber passing through urban toll stations, they systematically omitted local, non-merchant timber harvesting destined for regional shipyards. The presence of newly felled Pomeranian oak within the Gdansk hull framing demonstrates that maritime shipbuilding infrastructure maintained operational continuity by shifting from imported pine to local hardwoods. Thus, the Gdansk vessel's framing timbers serve not to refute the reality of demographic decline, but to illustrate how regional shipbuilders dynamically adapted material sourcing during broader macroeconomic disruptions.

Which of the following best describes the primary function of the reference to 'the vessel's framing timbers' in the first paragraph?

During the early nineteenth century, the manufacture of high-grade optical glass for astronomical telescopes was severely constrained by the inability to eliminate density variations, known as striae, in large molten batches of crown and flint glass. Pierre-Louis Guinand, a Swiss artisan, revolutionized optical glass production by introducing a stirring mechanism constructed of fireclay cylinders into the molten crucible. This technique disrupted the thermal stratification and chemical heterogeneities that typically produced light-refracting imperfections upon cooling. Recognizing the potential of Guinand's innovation, the Bavarian entrepreneur Joseph von Utzschneider recruited Guinand to the Benedictbeuern glassworks, where he collaborated with the physicist Joseph von Fraunhofer. While Guinand focused primarily on mechanical homogenizing methods, Fraunhofer systematically analyzed how chemical compositions affected refractive index and dispersion. Crucially, Fraunhofer discovered that adding precise quantities of lead oxide to flint glass batches not only lowered the melting point but also heightened chromatic dispersion, whereas adjusting potash concentrations in crown glass stabilized optical clarity. However, Fraunhofer's paramount technical breakthrough—the precise mapping of dark absorption lines in the solar spectrum—relied explicitly on Guinand’s fireclay-stirred discs, which provided unprecedented homogeneity in large-diameter lenses.

According to the passage, Fraunhofer’s discovery regarding the addition of lead oxide to flint glass batches indicated that this substance produced which of the following effects?

In forest ecology, the role of mycorrhizal fungi in facilitating inter-plant nutrient transfer was long believed to depend solely on concentration gradients between donor and recipient trees. However, recent investigations into the rhizospheric microbiome have highlighted the modulating role of mycorrhizal helper bacteria (MHB). Rather than merely accelerating hyphal elongation, specific strains of MHB synthesize volatile organic compounds (VOCs) that alter the permeability of fungal cell walls. Specifically, by suppressing the activity of fungal chitin synthase, these bacterial VOCs increase fungal membrane fluidity, thereby elevating the rate of passive glucose transport from host plant roots into the fungal sheath. Crucially, this mechanism operates independently of the host plant's photosynthetic rate, disproving the earlier assumption that fungal carbon uptake is exclusively regulated by host sugar availability. Moreover, while previous models posited that mycorrhizal networks uniformly distribute carbon among interconnected saplings, empirical measurements demonstrate that MHB-mediated transport selectively favors saplings colonized by ectomycorrhizal species over those associated with arbuscular mycorrhizae, due to differential binding affinities of the bacterial VOCs for fungal surface lectins. Consequently, in mixed-species stands, MHB activity creates localized carbon sinks that alter competitive dynamics among understory vegetation.

According to the passage, the volatile organic compounds synthesized by mycorrhizal helper bacteria directly influence fungal carbon uptake by doing which of the following?

In oceanographic research, the efficiency of the biological carbon pump—the process by which surface organic matter is sequestered into the deep ocean—has traditionally been estimated using temperature-dependent models of microbial remineralization. These classic models operate on the premise that the rate at which sinking particulate organic carbon (POC) is degraded in the mesopelagic zone ($200$–$1000$ meters) is governed primarily by ambient water temperature, which regulates bacterial metabolic rates. Consequently, higher mesopelagic temperatures are assumed to correspond directly to rapid carbon attenuation and lower long-term sequestration efficiency.

However, recent deep-sea observational data challenge this single-factor paradigm by highlighting the role of diel vertical migrators (DVM)—zooplankton that feed at the surface by night and retreat to mesopelagic depths by day. DVM organisms actively transport carbon downward, releasing metabolic byproducts directly into deep waters and thereby bypassing upper-layer microbial degradation. Crucially, the transport efficiency of DVM varies significantly by taxonomic composition: while crustacean migrators release primarily dissolved excretions that remain vulnerable to mid-water microbial breakdown, gelatinous migrators produce dense, membrane-bound fecal pellets that sink rapidly past the mesopelagic threshold before microbial decomposition can occur.

Because standard carbon-budget models rely on mesopelagic microbial respiration rates as a uniform proxy for total carbon turnover, they generate significant predictive errors. Specifically, in high-temperature maritime zones where crustacean populations are minimal but gelatinous migrators abound, standard models project substantial upper-ocean carbon retention, whereas empirical measurements reveal deep-sea carbon flux rates exceeding model predictions by more than $40\%$.

Based on the passage, which of the following can be most logically inferred regarding the predictive errors of standard carbon-budget models in high-temperature zones dominated by gelatinous migrators?

Read the following sentence from a historical study on soil conservation practices:

"While early twentieth-century agronomists maintained that continuous leguminous crop rotation would permanently replenish soil nitrogen levels without degrading mineral trace elements, subsequent long-term soil assays demonstrated that prolonged monocultural legume planting accelerates the acidification of subsoil strata, thereby reducing the bioavailability of essential micronutrients such as molybdenum."

Based on the sentence above, which of the following can be most reasonably inferred regarding prolonged leguminous crop cultivation?

For decades, soil scientists believed that Amazonian soils were universally infertile, depleted of organic nutrients by centuries of intense tropical weathering and leaching. However, the discovery of extensive deposits of Terra Preta de Índio ('Indian dark earth') across the Amazon Basin has challenged this long-held paradigm. Unlike the surrounding nutrient-poor oxisols, Terra Preta exhibits extraordinary fertility, characterized by high concentrations of persistent organic carbon, nitrogen, phosphorus, and calcium.

Recent archaeological and pedological analyses indicate that Terra Preta is not a naturally occurring soil type, but rather an anthropogenic product created by pre-Columbian Indigenous populations between 500 and 2,500 years ago. These ancient agriculturalists systematically enriched the soil through the controlled addition of biochar—a stable form of charcoal produced by low-temperature pyrolysis of organic waste—along with animal bones, fish remnants, and potsherds. The porous micro-structure of biochar acts as a molecular sponge, dramatically increasing the soil's cation exchange capacity (CEC). Consequently, Terra Preta retains essential plant nutrients and prevents them from being washed away by heavy rainfall, allowing nutrients to persist in the soil matrix for centuries without significant degradation.

Moreover, researchers have identified distinct microbial communities within Terra Preta that actively cycle nutrients and enhance soil resilience. While neighboring oxisols rapidly lose fertility after just a few crop cycles following clearing, Terra Preta fields maintain high agricultural yields indefinitely without requiring chemical fertilizers. Modern agronomists are currently examining the biochemical composition of Terra Preta to develop sustainable soil amendment strategies aimed at restoring degraded tropical soils worldwide.

According to the passage, the dramatic increase in Terra Preta's cation exchange capacity is explicitly attributed to which of the following factors?