1. 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 speculation 后面的从句是不是that 和whether 都可以引导，一定都要求是虚拟语气吗？如这里的may have been

这里的may have been不是虚拟语气吧，如果是，好象应该是might

但speculation后面的同位语从句能否用whether引导，我也想知道。

up

thanks a lot !!