（中考英语）--Is Maria knocking at the door

（中考英语）--Is Maria knocking at the door
--Is Maria knocking at the door
--It( )be her.She is in Australia now.
A.mustn't B.can't
可是我觉得A也可以,因为题目中已经说了“Maria现在在澳大利亚”,所以A应该也可以用吧,表示一定不是她.