GMAT Sentence Correction (SC) | Re: Carnivorous mammals can endure what would otherwise be

In general which is preceded by comma , So eliminated all option with 'which'

Carnivorous mammals can endure what would otherwise be lethal levels of body heat because they have a heat-exchange network which kept the brain from getting too hot.
a) which kept (incorrect)
b) that keeps (Correct)
c) which has kept (Incorrect)
d) that has been keeping (incorrect)
e) having kept (wordy also not in same tense as non underlined part)

Hope that helps
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