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Question

Difficulty: MediumSelecting Concluding Sentences and Transitions

Passage:

In 1964, radio astronomers Arno Penzias and Robert Wilson were using a large horn antenna in Holmdel, New Jersey, to detect weak radio waves bounced off balloon satellites. To their frustration, they kept detecting a persistent, low-level hum in the microwave spectrum that seemed to come from all directions in the sky. They spent months checking their equipment, going so far as to clean out nesting pigeons and their waste from the horn, but the static remained. Ultimately, this mysterious noise was identified not as a technical malfunction, but as the cosmic microwave background radiation—the relic radiation left over from the Big Bang.

The writer wants to add a concluding sentence at the end of the passage to emphasize the significance of the scientists' discovery. Which of the following sentences best accomplishes this goal?

  1. A
    Consequently, they went on to win the 1978 Nobel Prize in Physics, which they shared with Pyotr Kapitsa, whose research focused on low-temperature physics.
  2. This accidental discovery provided the first direct observational evidence for the Big Bang theory, fundamentally transforming our understanding of the universe's origin.Answer
  3. C
    Instead, this groundbreaking discovery settled a long-standing debate among astrophysicists, it proved that the universe did indeed have a hot, dense beginning.
  4. D
    For instance, although they only sought to study satellite signals, this unexpected static will reshape the field of astronomy.

Answer

The sentence that describes the accidental discovery providing the first direct observational evidence for the Big Bang theory, fundamentally transforming our understanding of the universe's origin.
The correct option is the sentence stating that the accidental discovery provided the first direct observational evidence for the Big Bang theory. This sentence summarizes the historical significance of the discovery described in the passage and connects directly to the mention of the Big Bang without introducing unrelated details.

Step-by-Step Solution

1
Analyze the main focus of the passage.
The passage describes the accidental discovery of cosmic microwave background radiation, which is the relic radiation from the Big Bang.
Understanding the core topic of the passage is necessary to determine what information a concluding sentence should summarize or emphasize.
2
Evaluate each option for grammatical correctness and logical flow.
Identify that the option containing a comma splice is grammatically incorrect, and the option with a future tense shift is inconsistent with the historical narrative. The option discussing Pyotr Kapitsa introduces irrelevant details.
ACT questions often test multiple grammatical and rhetorical skills simultaneously, so eliminating grammatically flawed options narrows down the choices.
3
Choose the option that best concludes the passage by emphasizing its significance without introducing unrelated details.
The sentence emphasizing the direct observational evidence for the Big Bang theory is chosen because it logically concludes the narrative about the discovery's significance.
An effective conclusion must wrap up the main point of the passage and connect back to its central thesis.

Key Concept

Selecting effective concluding sentences that align with the passage's main thesis.
Estimated Time:1m 0s
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Topics

Selecting Concluding Sentences and Transitions

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