PSAT Writing and Language Question 139: Answer and Explanation

Question: 139

Which sentence most effectively establishes the central idea?

• A. NO CHANGE
• B. The object of testing the DNA is to re-create many strands of the DNA in question.
• C. Saunders uses a variety of machines in order to analyze the DNA.
• D. Saunders would be unable to identify the DNA without the thermocycler.

Correct Answer: A

Explanation:

A

Difficulty: Medium

Category: Development: Introductions and Conclusions

Getting to the Answer: Read the entire paragraph and then put each answer choice at the beginning. Choose the one that makes the most sense and is further explained by subsequent details in the paragraph. The paragraph discusses the process of identifying DNA, which is lengthy and involves changing the temperature of the DNA several times. Choice (A) is closest to this summation of what is to follow and is the correct answer.