A) wrong because of it (no antecedent). Can be the "impersonal" it, such as "it is sunny?
(a) "as it is with..." isn't parallel to anything. this is the main problem.
nothing "is with" online drugstores, so this choice is not sufficiently parallel.
B) I do not why is it wrong. Is it because of the parallelism?
"with the case of" is an incorrect rendering of "as is the case...".
(it's possible for "with the case of" to be correct, but the preposition "with" would have to make sense, AND you'd have to be literally talking about "the case of" something.
for instance:
the lawyer made history with the case of X, as with the case of Yunlike this example, the problem in this thread doesn't satisfy either of these requirements)
C) Correct. "As is......prescriptions are...."
correct, in that "is" and "are" have to be in the same tense.
you may not, however, understand the full scope of the usage of "was/is the case". for more details on that, see the posts that come earlier in this thread.
D) Distorts the meaning: It says that traditional pharmacies "are" online drugstores
that's one way to read it, yes. and that'd be wrong.
the other way to read it is as a comparison (as intended). it'd still be wrong, though, because you can't use "as" with only a noun.
E) Wrong because of LIKE. The cornerstone are not similar to traditional pharmacies.
good.
Is correct "the cornerstone...IS prescriptions" or "the cornerstone.....ARE prescriptions"?
if you have NOUN is/are NOUN, then the noun that comes BEFORE the verb is the subject.
so, you'd say
the cornerstone IS prescriptions, but you'd say
prescriptions ARE the cornerstone.