OG15 第12题求助

我要喝可乐

12 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
(B) that keeps
(C) which has kept
(D) that has been keeping
(E) having kept



正确答案选B
OG的解释中说C “has kept indicates a more definite context and time preiod and suggests that the heat－exchange network may no longer have this effect
可是现在完成时不是表示从过去某一个时间点开始发生的动作持续到现在或者对现在造成影响么，为啥在这里说感觉network 不再有这个功能了呢？