15: Reptiles, by drawing their body heat directly from the Sun rather than burning calories to generate it, can survive on ten percent of the nourishment that a mammal of similar size would normally require

A: rather than burning calories to generate it

B: rather than the generation of body heat by burning calories

C: and not from generating it by burning calories

D: instead of by burning calories for generating it

E: instead of body heat generated by burning calories

还没有标准答案，我怎么看谁都有问题？如果选择a,怎么可以漏掉by?

求教。xiexie