OG12中，语法第10题的解释有些看不懂，大家帮忙瞅瞅阿……
Carnivorous mamals 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.
解释如下：The use of the past tense (kept) is incorrect because a current situation is discussed; the present tense
(keeps) is consistent with the other verbs in the sentence. In (A) and (C), which introduces a restrictive clause. some writers follow the convention that which can only be used for nonrestrictive clases, but insistence on this rule is controversial, and both (A) and (C) can be rejected on other grounds.
后面说which引导限制性从句，后面的意思是....
