must have done 表推测时,附加疑问句该怎么样用?

依据一条简单的规则:把该句变成真实的语气,再根据真实的语句使用附加问句,如:
1.It must have rained last night,_____?
真实句It rained last night.再附加问句didn't it?所以答案为didn't it?
2.She must have seen the film before,_____?
真实句She has seen the film before.再附加问句hasn't she?所以答案为hasn't she.