It was impossible for the whales to escape and move south --------/?

问题描述:

It was impossible for the whales to escape and move south --------/?
No.it is not .The ice stretched for kilometers aroud them .
A.was it B.was not it C.were they 为什么?

B,反义疑问句和主句是相反的,主句是肯定句,那么反义疑问句就是否定句
主句的主语是it,那么反义疑问句的主语也是it
时态是过去式,所以是 was not it?
也可以根据答句的主语判断.