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Difficulty: MediumEstablishing Introductions and Thesis Statements

The following is an excerpt from a draft of an essay about the cosmic microwave background radiation.

[1]
__________________________________________________. In 1964, radio astronomers Arno Penzias and Robert Wilson were troubled by a persistent, low-frequency hum coming from their Holmdel horn antenna in New Jersey. They tried everything to eliminate the noise: pointing the antenna in different directions, cleaning out nesting pigeons, and cooling the receiver to near absolute zero. Yet, the hiss remained constant, day and night. Ultimately, they realized that this background noise was actually the cosmic microwave background radiation—the leftover thermal echo of the Big Bang. Their accidental discovery provided the first definitive observational evidence for the Big Bang theory, transforming our understanding of the universe’s origins.

Which choice best establishes the main topic and serves as an effective introduction to the essay?

  1. A
    Penzias and Wilson were just trying to improve radio communications, they accidentally discovered the echo of the Big Bang.
  2. B
    Although radio astronomers in the mid-twentieth century were searching for a clean communications channel.
  3. A search for a clean communications channel unexpectedly yielded the most crucial evidence for the origins of our universe.Answer
  4. D
    Radio antennas are highly sensitive instruments that require careful maintenance to prevent interference from nesting birds.

Answer

The statement that describes a search for a clean communications channel leading to crucial evidence for the origins of the universe is the correct choice.
The statement describing how a search for a clean communications channel led to evidence for the origins of the universe is correct. It is grammatically correct and successfully introduces the dual nature of the passage: the practical context of Penzias and Wilson's research and the ultimate scientific breakthrough concerning the Big Bang.

Step-by-Step Solution

1
Analyze the passage to determine its main focus and theme.
The passage discusses how Arno Penzias and Robert Wilson accidentally discovered cosmic microwave background radiation (the thermal echo of the Big Bang) while trying to clean up radio noise on their antenna.
An effective introduction must establish the main topic, linking the search for clean radio communications to the monumental cosmological discovery.
2
Evaluate the grammar and structure of each option to eliminate grammatically incorrect options.
One option contains a comma splice, and another is a sentence fragment. These are eliminated from contention.
ACT English questions require the correct choice to be grammatically correct.
3
Compare the remaining grammatically correct options for relevance and scope.
The option about antenna maintenance is too narrow and misses the main point of the essay. The option linking the clean communications channel search to the origins of the universe sets up the narrative and thesis perfectly.
The correct introduction must match the rhetorical goal of the passage as a whole.

Key Concept

Establishing Introductions and Thesis Statements
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Topics

Establishing Introductions and Thesis Statements

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