Complete Question Explanation
Must Be True. The correct answer choice is (B)
This question tests your ability to draw proper inferences from two opposing explanations of an
observed phenomenon. The stimulus begins with the words “A study claims”, which is a very common
way for the test makers to introduce contrasting viewpoints in a Logical Reasoning question. Both the
study and the author of the stimulus agree that the “average temperature each year for the last five years
has been higher than any previous yearly average on record.” The study uses this evidence as a premise
in support of the claim that “the average temperature on Earth has permanently increased,” while the
author points out that even ten years of average temperatures which are record highs may be merely
random and would not be sufficient to conclude that the increase has become permanent. Answer choice
(B) correctly expresses this conclusion.
Answer choice (A): This answer choice is an exaggeration and over-generalization. The stimulus does
not address all increases in average temperature on record, nor does it preclude the possibility that a
large increase in average temperature has at sometime occurred from one year to the next. Remember,
in a Must be True question the correct answer choice will present information that is addressed in the
stimulus, and cannot provide details that the stimulus does not mention.
Answer choice (B): This is the correct answer choice. Answer choice (B) is most strongly supported
by the information above, as it states that five years of higher than average temperatures does not
necessarily mean that those higher temperatures are permanent.
Answer choice (C): This answer choice attempts to trick the reader into viewing the author’s premise as
a prediction of future circumstances. Just because random fluctuations in temperature can account for up
to ten consecutive years of record high temperature does not necessarily mean that any five such years
will be followed by five more. Attentive readers should have no difficulty dismissing this answer choice.
On a related note, be particularly wary of any attempt by the test makers to make a definitive prediction
about the future. These predictive efforts are almost always flawed and should be viewed accordingly.
Answer choice (D): Answer choice (D) is the most attractive of the incorrect answer choices, but it
is inaccurate and incomplete. The author notes that random fluctuations in temperature are always
occurring, and that periods of higher than average temperatures can still be considered random, but the
stimulus does not indicate how long these random fluctuations “typically” last.
Answer choice (E): Like answer choice (A), this answer choice goes too far. The stimulus makes no
mention of whether the average temperature of the Earth could ever increase due to something other than
random fluctuation. Further, the tentative word choice in the author’s explanation (“up to ten years”, “are
often…part of”) is sufficient to indicate that the correct answer choice will likely also be tentative. The
absolute phrasing of this answer choice is enough to quickly eliminate it from further consideration.