Hello, everyone. For what it is worth, I feel as if (C) is a stronger answer than (D). Why? Because the non-underlined portion references
their own reported levels of involvement. The sentence, then, seems to draw attention to an unnamed interpreter of such information, and a quick rearrangement of the two major pieces of the sentence reveals why
through is stronger than
by. The sentences, rearranged, with much of the "fluff" removed:
(C)
Through their own reported levels of involvement, the way in which Taylor and the other participants moved was determined.(D)
By their own reported levels of involvement, the way in which Taylor and the other participants moved was determined.Do I think the sentence would appear as is on the GMAT™? No. But does that mean it cannot or should not be studied for some related purpose? Again, I would say no. The split I have drawn attention to above is a legitimate one, one that leans on the expressed meaning of the sentence, and that is definitely something that GMAT™ SC concerns itself with.
I hope that helps. Good luck with your studies.
- Andrew