PSAT Writing and Language Question 339: Answer and Explanation

Question: 339

Which choice, if added here, would most effectively introduce the main topic of the paragraph?

• A. NO CHANGE
• B. Gause's results confirmed the theory.
• C. It is important for scientific experiments to contain control groups.
• D. Gause eventually published his results in a book.

Correct Answer: B

Explanation:

Note the question! The question asks which choice introduces the main topic of the paragraph, so it's testing consistency of ideas. Determine the subject of the paragraph and find the answer that is consistent with that idea. The paragraph discusses the results of Gause's experiment, which proved the validity of the theory of competitive exclusion. Eliminate (A) because Gause's experiment confirmed, not contradicted, the validity of the theory, which had been hypothesized previously by scientists. Keep (B) because it is consistent with the subject of the paragraph. Eliminate (C) because the importance of control groups to scientific experiments is not consistent with the results of Gause's experiment. Eliminate (D) because Gause's publication of his results does not convey the significance of his experiment. The correct answer is (B).