Some insects are able to feed on the leaves of milkweed, a toxic plant

OFFICIAL EXPLANATION

C is the correct answer. It is impossible to argue logically that the insects’ method of detoxification by cutting and draining guarantees that some insects will always be able to eat milkweed without assuming that for some reason that toxin-carrying veins of the milkweed can never evolve to become so strong that they would thwart the insects’ attempts to cut through them.

A is incorrect. The passage does not make any claims about plants other than mildewed. The insects that detoxify mildewed by cutting veins might evolve an ability to detoxify other plants without this affecting anything relevant to the argument offered about their ability to eat mildewed. The second answer choice is incorrect. The passage is not concerned with other types of toxic plants and makes no assumption about them. The fourth answer choice is also incorrect. The method of detoxification used by the insects on milkweed might also be used to detoxify other plants without this affecting anything relevant to the argument offered about the insects’ ability to eat milkweed. The fifth answer choice is incorrect. It may be true that there are insects that use means other than draining toxins in order to feed on toxic plants, but the conclusion drawn in the passage does not depend on there being any such insects.