请教prep-3的28题

nanawo

According to one expert, the cause of genetic irregularities in many breeds of dog is not so much that dogs are being bred for looks or to meet other narrow criteria as that the breeds have relatively few founding members.

(A) the cause of genetic irregularities in many breeds of dog is not so much that dogs are being bred for looks or to meet other narrow criteria
(B) the cause of genetic irregularities in many breeds of dog is not as much their being bred for looks or meeting other narrow criteria as much
(C) it is not so much the cause of genetic irregularities in many breeds of dog that they are being bred for looks or meeting other narrow criteria as much
(D) it is not so much that the cause of genetic irregularities in many breeds of dog is their being bred for looks or meeting other narrow criteria so much
(E) it is not so much the cause of genetic irregularities in many breeds of dog to be bred for looks or to meet other narrow criteria
答案A，用排除法可以选出，但是对于not so much ...as的用法一直很模糊，不知哪位牛牛可以解答一下啊

biantaishabi

这里是so much that... as that ... 的平行结构