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[quote="ranjeet75"]Few insects are able to feed on the leaves of silkweed, a toxic plant, by first cutting and draining the vein that secretes the toxin. This method of detoxification guarantees that some insects will always be able to eat silkweed, because the plant could never evolve to produce a toxin that is lethal in the trace amounts left after the vein is cut.

The argument depends on which of the following assumptions?

A. The insects that successfully detoxify silkweed are not able to undergo the evolutionary changes necessary to allow them to detoxify other plants.
B. Unlike silkweed, other kinds of toxic plants would be able to overcome their vulnerabilities to predators through evolutionary changes.
C. The toxin-carrying veins of the mildewed plant can never evolve in such a way that insects cannot cut through.
D. The method of detoxification used by insect predators of mildewed would not successfully detoxify other kinds of toxic plants.
E. There are insects that use means other than draining the toxin in order to feed on toxic plants.

The Argument has the conclusion that "This method of detoxification guarantees that some insects will always be able to eat silkweed, because the plant could never evolve to produce a toxin that is lethal in the trace amounts left after the vein is cut." The conclusion is based on the argument that the Plant will never evolve to produce a toxin that i lethal in the trace amt left after the vein is cut." What if the Plant evolves a technique that makes it impossible for the insect to cut the vein carrying lethal toxins. In this case the conclusion given by the author would be deemed senseless. Hence we need to assume that the "The toxin-carrying veins of the mildewed plant can never evolve in such a way that insects cannot cut through." to make the conclusion valid.
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Is there a spelling mistake in the argument typed?

The argument talks about Silkweed plant. Only once answer choice mentions the Silkweed plant, and rest others, including the OA, talk about some other plant, Milkweed.

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Negation of (C): The toxin-carrying veins of the mildewed plant can evolve in such a way that insects cannot cut through ---> negation destroys the conclusion and therefore is a necessary assumption for the argument.

hope this helps