thx querio for the input!
it is always easy to justify when you know the correct answer!
I gotta change my strategy of posting questions.
I actually think that "C" is wrong because:
....because of food supplies , which were dwindling...
is ackward and wordy
assuming the rest of the sentence is Ok, it could be corrected as: ...because of dwindling food supplies...
but because we dont have this version, we go for B.
Well, when I know the answer, I can find every reason to justify it and discard the others