857 There is speculation that increasing cold weather was what may have been responsible for the Anasazi move from Mesa Verde to sites in other canyons.

(A) that increasing cold weather was what may have been

(B) whether increasing cold weather was what was

(C) that increasingly cold weather was what had been

(D) whether increasingly cold weather may have been what was（E）

(E) that increasingly cold weather may have been

请问C错在哪里？

1、过去完成时单独使用，不正确

2、题干中表示可能的情态动词一般不要省略，省略后改变原句意思了

3、was what had been太罗嗦了