Q:that must be a mistake 为什么回答是NO,it can't be.而不是no,it can't?

问题描述:

Q:that must be a mistake 为什么回答是NO,it can't be.而不是no,it can't?
我打得太快,没有分大小写

这句话的主语是it,但真正动词是be.can是助动词
所以要么说 it can't be;要么说 it is not.