Because they had been living in the mountains for a number

E) is the best answer here, but it's still not ideal. If this were a real GMAT problem there would be a comma between “this fact” and “when” in answer (E), because “when combined with their do-or-die will power” is a non-restrictive modifier (that is, not essential to the meaning of the sentence). As others have pointed out, the correct verb form is “combined” (in the past tense), rather than the gerund “combining” (which gives you very little information about the time frame of the action described). You can see this more easily if you disregard the non-restrictive modifier—just pretend it’s not there so you can more easily examine the subject-verb pair.

What hasn’t been mentioned yet is that (A), (B), and (C) are wrong because “a fact” seems like it modifies “terrain,” which doesn’t make much sense. This ambiguity is enough to eliminate the first three answer choices.

am with you that this question suck
But I dont understand how is it E grammatically right?
In E, from what I know WHEN is adverbial modifier(same as although), when ADV modifier is attached to the middle of the sentence, it has to be attached to a clause not a noun phrase, otherwise it would ungrammatical. And what it seems to me that the comma before THIS FACT is trying to attach two independent clauses(but there is only one) otherwise the comma is not justified.
One more question: COMBINING in A is an adjective meaning it doesn't have tense, so it doesn't show the time frame of the action.

May I seek a small clarification from Mimi?

Mimi has said that that there has to be a comma between fact and when, because “when combined with their do-or-die will power” is a non-restrictive modifier (that is, not essential to the meaning of the sentence).

When I coined the passage, I precisely wanted to make it restrictive and hence deliberately left out the comma. Let us say, if the sentence had a comma as Mimi suggests, it would run as this with an in-built parenthesis.


and this fact, when combined with their do or die will power, made

Now, if you remove the parenthesis momentarily because it is not essential to the crux of the passage, then according to me, the meaning gets substantially altered. To make them a dreaded lot, you require two things i.e., firstly, the fact that they knew the pulse and beat of each and every corner of the terrain …… and secondly, this fact’s combination with their do or die will power. If the second thing was not there, they would not be considered a dreaded lot

If this was the underlying thought, would GMAT have used a comma? I look forward to some comments.

Secondly, a fact in Choices A, B and C does not modify terrain. If it were to modify terrain, a relative pronoun such as which with preceding comma or that without a preceding comma would have been used. In the given case, a fact stands for the liberation forces’ knowledge of the pulse and beat of each and every corner of the terrain. A, B and C have the problem of using “combining”

Clarifications gladly given! My comments are directed as much at the strategy you should use to approach this problem as at the grammar itself.

If it's a non-restrictive modifier, then there should be two commas. If it's a restrictive modifier, then there should be no comma after "will power." Remember that a comma does not indicate a pause in a sentence when you speak it out loud. It has grammatical significance. To fully integrate a restrictive modifier into a sentence, you generally do not follow it up with a comma. However, since the GMAT does not test commas directly, this isn't a big issue.

With respect to "a fact": it is indeed an appositive modifier. My point is that the GMAT prefers an appositive modifier to modify what is immediately next to it, i.e., terrain. Technically "a fact" here may stand in apposition to the entire clause "the rebellious forces...knew," but the GMAT usually avoids that kind of ambiguity. That knowledge can help people decide to eliminate A), B), and C).

Hope that helps! It's a good problem that raises lots of subtle issues!

Thanks a ton Mimi, but only one thing that I want to know fo sure is that, if the GMAT so explicitly prefers an appositive modifier to modify what is immediately next to it, i.e., terrain ( in this issue, what is immediately before it). then it must have said so in some concrete cases. May I know them for my info please?

Thanks again for your wonderful inputs.

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