GMATprep里的题

There are hopeful signs that we are shifting away from our heavy reliance on fossil fuels:  more than ten times as much energy is generated through wind power now than it was in 1990.

(A) generated through wind power now than it was

(B) generated through wind power now as it was

(C) generated through wind power now as was the case

(D) now generated through wind power as it was

(E) now generated through wind power than was the case

为什么D里面的it不能指代 energy generated through wind power？

这种对比的题都不能用it 因为it是有明确指代对象的 比如这里面就是指代现在generate出来的energy

现在generate出来的energy不可能was in 1990.  只能用that 那之类 或是 the case

明白了，谢谢！！