Dr Khan: Professor Bums recognizes that recent

Must Be True. The correct answer choice is (C).

The stimulus presents a series of observations made by Dr. Khan regarding Professor Burns. An overt argument is never stated. Since the distinction between fact and opinion is crucial on the GMAT, especially in Must Be True stimuli where the correct answer choice must satisfy the strict parameters of the Prove Test, it is important to analyze each claim as follows:

Earlier observations showed a comet reservoir far out in the solar system, but recent observations cannot confirm this. (Fact)
Professor Burns interprets the recent observations as proof that the comet reservoir doesn’t exist. (Opinion)
The recent observations occurred under poor conditions. (Fact)

Note the use of double negatives in the second sentence of the stimulus: According to Prof. Burns, “this non-confirmation is enough to show that the earlier observations are incorrect.” It is imperative to immediately simplify this statement by removing both negations and distill its meaning: Burns doesn’t believe there is a comet reservoir far out in our solar system. However, since the recent observations occurred under poor conditions, it would be reasonable to doubt their significance: while they cannot prove (or disprove) the existence of a comet reservoir either way, they certainly cast doubt on Professor Burns’s conclusion. In other words, such a reservoir could exist. This prephrase agrees with answer choice (C).

Answer choice (A): Whether the recent observations, if made under good conditions, would have provided conclusive evidence of a comet reservoir is impossible to know. Beware of hypotheticals and speculative claims when answering Must Be True questions: more often than not, such claims are impossible to prove.

Answer choice (B): Just because Professor Burns reached an invalid conclusion does not mean that the recent observations actually confirm the earlier ones, i.e. that a comet reservoir exists. As stated earlier, it is impossible to know from the information provided whether or not such a reservoir actually exists. This answer choice conflates fact and opinion, and is therefore incorrect.

Answer choice (C): This is the correct answer choice. All we know from the facts presented in the stimulus is that the recent observations do not provide a suitable basis for rejecting the earlier ones. Professor Burns, who believes otherwise, is clearly wrong in making her assessment. In other words, her claims about the implications of the recent observations is incorrect—a comet reservoir could exist (we just don’t know).

Answer choice (D): As with answer choice (A), we have a hypothetical, speculative claim that cannot be proven with absolute certainty. It is entirely possible, however unlikely, that if the recent observations had been made under good conditions, they would have been enough to disprove the earlier ones.

Answer choice (E): This answer choice contains an exaggeration (“worthless”) that cannot be substantiated with the information provided. Eliminate.