Can you kindly confirm why A is wrong? Is it because of wrong usage of including or unidiomatic threat from?
the parallelism in that option doesn't make sense.
in that wording, the two parallel elements are "threat" and "(declining) sales". this is incorrect: the sales themselves are not a challenge facing the company.
to be sufficiently accurate, the sentence should state that the decline
in sales, not the sales themselves, poses a threat.
Also, C can we say usage of both include and among causes redundancy.
note that this question was answered 2 posts before yours; please read the thread in its entirety before posting. thanks.
Also, from one of GMAT official blog, I figured that GMAT has removed/ atleast removed idioms from their test questions, do we still need to remember such idiom list??
i believe that idioms could still be tested, if the particular choice of idiom has a fundamental effect on the meaning of the sentence.
on the other hand, the test writers have an explicitly stated goal of NOT writing problems that can simply be solved by memorization (in fact, they wrote this in that very same blog post), so i don't imagine you're going to be seeing many problems that will test idioms that don't affect the context of the sentence.