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.
7.Carnivorousmammalscan endure what would otherwise be lethal 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
for 1) 对其它哺乳动物来说是致命的体温 for 2) You use otherwise before stating the general condition or quality of something, when you are also mentioning an exception to this general condition or quality. excerpt from Collins dictionary item 2