In 1646, William Stafford published The Reason of the War, with the

Official Explanation

Creating a filter: if we don't draw any immediate conclusions from the prompt, we can go to the answer choices.

Finding objective defects: the answer choices naturally fall into two groups, one containing (A) and (B), and the second containing (C) through (E). We have to be careful about the modifying phrase that starts with "arguing" in the original sentence. It's unclear in its reference, because it comes after and therefore modifies the pamphlet, but says "arguing in a pamphlet" as if modifying Stafford. Better to have it clearly modify the pamphlet. That decision limits us to (C) through (E). Choice (C) uses the phrase "powers from"; this is non-idiomatic English without a verb prior to "powers." You could say you "advocate a transfer of power from X to Y," but to say you "advocate power from X" isn't sensible English. Choice (C) is further twisted because the powers are identified as "parliamentary" in a way that doesn't make it clear that they are initially not parliamentary. So (C) is out. Choice (D) has a good feature, which is to introduce the thing being advocated in a clause after the word "that"; we generally favor that construction. But here, that construction is not parallel with the phrase "and for peace..." later in the sentence. Choice (E) is parallel in that way: the pamphlet argues for one thing and for another.

The correct answer is (E).

I am not sure about this answer. Can any expert pitch in and explain it?

The arguments given in the pamphlet need to be presented in parallel. E accomplishes this by by stating the pamphlet "argued FOR Charles I..." and "FOR peace....".

A & B make it seem like the English Subject was the one arguing.
C & D are not parallel.

Answer: E

A. Incorrect because verb-ing action modifier modifies previous action. And out here publishing is not the reason of arguing.
B. Incorrect because verb-ing action modifier modifies previous action. And out here publishing is not the reason of arguing.
C. Incorrect because list compared using "and" conjunction is not parallel
D. Incorrect because list compared using "and" conjunction is not parallel
E. Correct , its a noun+noun modifier which correctly modifies book i.e. noun from previous clause and last two entity joined by and conjunction are in parallel list.