Bunuel
The destruction of the rain forests means
exterminating plants that had the potential to cure people of life-threatening illnesses.
A. exterminating plants that had the potential to cure people of
B. exterminating plants that have the potential to have cured people of
C. the extermination of plants that have the potential to cure people of
D. the extermination of plants that had the potential to cure people from
E. the extermination of plants that might have had the potential to cure people of
VERITAS PREP OFFICIAL SOLUTION:
Whenever you see answer choices using different verb tenses (as you see "had" vs. "have" here), you should look to eliminate verb tenses that would create an illogical timeline. Here, several choices are guilty of such a timeline.
With (A), (D), and (E) note that the past tense "had" suggests that the plants' ability to cure patients ended before the current extermination/destruction takes place. Note the use of "the destruction means..." which set the destruction/extermination in the presence. If the ability of these plants to cure anyone had already ended before the destruction/extermination there is no reason to write this sentence - the plants are a moot point!
Choice (B) is similarly illogical. The phrase "plants that have the potential to have cured" similarly puts the process of curing people further back in the past, which is even more illogical when you see that the plants' possession of that power is current (so they currently have the potential to have previously cured someone?).
Choice (C) matches the current status of the extermination/destruction with the present "have" and is therefore correct.