CP #7

From GMATHacks again.

Commensalism is any relationship between two living things in which one benefits and the other is neither helped nor harmed. Oxpecker birds are commensal species that flock with the large mammals of the African Savannah. They feed on ticks, fleas, and flies that are attracted to the mammals' fur. Which of the following, if true, can most reasonably be inferred from the statements above?
(A)	Oxpecker birds are neither helped nor harmed by the large mammals of the African Savannah.
(B)	Ticks, fleas, and flies are commensal species in their relationship with both oxpecker birds and the large mammals of the African Savannah.
(C)	No species exist in a commensal relationship with oxpecker birds except for large mammals of the African Savannah.
(D)	In commensal relationships, the smaller of the species in the relationship usually benefits while the larger is neither helped nor harmed.
(E)	Preying on small creatures drawn to the fur of the large mammals of the African Savannah does not significantly affect those mammals.

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Answer: E

This is an inference question. The passage suggests that, since oxpecker birds are commensal species with large mammals, they benefit from the creatures that are attracted to the mammals' fur, but the mammals themselves are neither helped nor harmed by the relationship. Consider each choice, looking for a reasonable inference:

(A) This choice gets the commensal relationship exactly backwards.
(B) This is clearly wrong. If oxpecker birds feed on ticks, fleas, and flies, clearly the ticks, fleas, and flies are neither benefiting nor neutral in their relationship with the oxpecker birds.
(C) This choice is too extreme. The passage only describes this relationship; it doesn't tell us that it is exclusive.
(D) This is also too extreme. It may be true in some instances, but the three sentences of the passage don't provide enough evidence to reasonably deduce this.
(E) This is correct. It merely restates the definition of commensalism in terms of the role of the mammals in their relationship with oxpecker birds.

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I know it's not a difficult question, but I've made the same sort of mistake on earlier questions too. I had used POE to come down to A & E. But, by then I had lost track of the question I guess, and chose A. A Veritas Prep GMAT Tip of the Week talks about such mistakes.