表猜测的反义疑问句希望各位高手能全面系统地给我讲一下另外 this place could have been beau

This place could have been beautiful,hasn't it?
This place could have been beautiful years ago,wasn't it?
当情态动词表推测时,它的反意疑问句的变法是要去掉情态动词,再看该用什么时态再用相应的时态反问．上面的两个句子中,第一个去掉情态动词后,没有时间状语,所以可以直接用现在完成时,也就是This place has been beautiful.而第二个去掉情态动词后里面有时间状语years ago,为一般过去时的时间状语,所以要变成一般过去时即This place was beautiful years ago.
再两个例子．
It must have rained last night,didn't it?It must have rained ,hasn't it
He may be doing his homework now,isn't he?