prep2-40,正确答案中的一个小知识点求教!

2. 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 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

A: correct

 请问A中的dogs are being bred ,为什么不是are bred 呢?或者直接是BEING BRED呢?

感谢回复!!!

刚看了语法书，好像是说一般进行的被动时态云云。。。

且听大牛们指教

谢谢楼上的回复,希望NN来给个更明确的答案