Questions 1-3 are based on the following passage:

    In nearly all human populations a majority of individuals can taste the artificially synthesized chemical phenylthiocarbonide (PTC). However, the percentage varies dramatically—from as low as 60 percent in India to as high as 95 percent in Africa. That this polymorphism is observed in non-human primates as well indicates a long evolutionary history which, although obviously not acting on PTC, might reflect evolutionary selection for taste discrimination of other, more significant bitter substances, such as certain toxic plants.
    A somewhat more puzzling human polymorphism is the genetic variability in earwax, or cerumen, which is observed in two varieties. Among European populations 90 percent of individuals have a sticky yellow variety rather than a dry, gray one, whereas in northern China these numbers are approximately the reverse. Perhaps like PTC variability, cerumen variability is an incidental expression of something more adaptively significant. Indeed, the observed relationship between cerumen and odorous bodily secretions, to which non-human primates and, to a lesser extent humans, pay attention suggests that during the course of human evolution genes affecting body secretions, including cerumen, came under selective influence.

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Question 1

It can be inferred from the passage that human populations vary considerably in their
 

(A)	sensitivity to certain bodily odors
(B)	capacity for hearing
(C)	ability to assimilate artificial chemicals
(D)	vulnerability to certain toxins found in plants
(E)	ability to discern bitterness in taste

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Analysis

The correct response is (E). In the passage's first paragraph the author points out that the ability to taste PTC varies among human populations, then in the final sentence of that paragraph refers to "other, more significant bitter substances...." It can reasonably be inferred from these two statements, considered together, that PTC is a bitter substance.

(A) is unsupported in the passage; in the second paragraph the author points out a correlation between earwax and odorous secretions, but neither states nor suggests that either has any affect on the sense of smell.

(B) is unsupported in the passage; in the second paragraph the author indicates that human populations vary in earwax type, but neither states nor implies that earwax type has any effect on hearing.

(C) grossly distorts the first sentence of the passage, which refers to the ability to taste one particular artificial chemical.

(D) finds some support in the passage, but this support is very weak. (D) relies on the unsubstantiated inference that since human populations vary considerably in their ability to taste bitterness, they must also vary considerably in their vulnerability to certain toxins in bitter-tasting plants. Moreover, without explicit support in the passage (D) is ambiguous in the use of "vulnerability," which might refer just to the body's vulnerability to toxins once they are ingested, or also to one's vulnerability to ingest a toxic plant--for lack of tasting the bitterness that warns of the plant's toxicity.