7. (B)
Question type: Assumption
(B) may be an unexpected answer, but it is nonetheless correct. It’s easy to assume that a herbal remedy won’t contain chemicals, but this isn’t a certainty.
The opposite of answer choice (B) would be "The herbal remedy contains chemicals." This would significantly weaken the argument _ a good indicator of the fact that the assumption was one that was necessary.
(A) is not relevant to the argument, since the conclusion has nothing to do with whether people will switch to herbal remedies or not.
(C) is not an assumption that the argument requires.
(D) is related to the argument in subject matter, but is not an assumption that the argument requires.
(E) is not an assumption that the argument requires.