B uses present continuous form, implying that the action is currently taking place. Rather than this implication, it would have been better if the answer choice had proceeded with the intended meaning.
"in order that " is incorrect. It implies that the mails, which were written, were in order. A total distortion of meaning.
Also the two parts,"boycotting and writing emails" are not simultaneous events. The actual meaning is that in order to protest, the mails were written.

A uses a verb+ing form after "comma". Whenever such happens, only two things can happen. They are:
i) the verb+ing is the consequence of the preceding clause.
ii) the verb+ing modifies the entire preceding clause.
Writing emails is NOT the result of "being in agreement to boycott the store".
"to take action AGAINST" is better than "to take action about".
Also "many were in agreement" is quite wordier. In simpler language, this idea can be mentioned as "many agreed to boycott bla bla bla".

E is quite similar to A in terms of wromng issues in that it is wordier, has verb+ing issue, and uses the clause "writing protest emails to the vice-president of the chain imploring him to take action against those hiring practices considered unsavory" which I feel is quite bad. "writing emails......imploring him..."together. STOP!

D- what is they referring to, "emails"????
The place of "in protest" implies that the vice-president of the chain, which is in protest.

C is the best among the answer choices.

Hope that helps.
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