The Federalist papers is a compilation of articles written by Alexande

To be honest, nikhilongc, I think the question deserves another tag: "Poor Quality" (in addition to a clarification on the source). I do not say this lightly. But whether we use because or since, the passive voice of the first half of the sentence does not align well with the latter half—the meaning is skewed. The sentence seems to want to express the following:

Because/Since X, Y, [and] Z were all advocates of the Constitution, they wrote a compilation of articles known as the Federalist papers.

However, the passive voice, in combination with as well as a few, places the explanatory clause in a tight spot. Is the emphasis on the authors or the compilation? Consider:

1) The Federalist papers is a compilation of articles written by [X, Y, and Z] because/since all of [the men] were advocates of the Constitution.

2) The Federalist papers is a compilation of articles written by Alexander Hamilton and James Madison, as well as a few [articles] by John Jay, because/since all of [the men] were advocates of the Constitution.

If the information about John Jay just said as well as John Jay, there would be less cause for confusion. But now we have broken up our list of authors with a second reference to articles, and that places more emphasis on the compilation than a well-written sentence would do. In general, we do not want to hit a phrase or clause in the middle of the sentence that reaches backward and forward at the same time. Notice how, once again, the active-voice sentence, along with a few cosmetic changes, would skirt the issue altogether, with a right-pointing logical progression of ideas throughout.

As for (C), them is not ambiguous once we reach the noun advocates. Articles can advocate (verb) an idea, but they cannot be advocates of one. Returning to my point from before, it is somewhat jarring, though, to hit them, anticipating further information about the articles, the closest plural noun (i.e. a few [articles]), but then encountering information about the authors instead. So no, ambiguity is not the issue, but lack of clarity is a problem. We should not have to go back and forth to qualify a pronoun. (E) is a safer option because it sidesteps the pronoun. The because/since split is a red herring as far as the GMAT™ is concerned. The only time I have seen since used incorrectly is when the sentence might also logically refer to a distinct point in time, as in, Since he wrote the paper, [main clause]. Would the continuation provide information about a subsequent chain of events, or would we understand that the introductory clause was meant to provide an explanation? Now that type of ambiguity would be grounds for elimination.

Anyway, those are my thoughts on the matter. I hope they prove of interest to you. (I always recommend sticking to official questions for Verbal practice.)

- Andrew