I me Mr Smith in the school library yesterday.--You are kidding .It --be him.He's gone back to
问题描述：
I me Mr Smith in the school library yesterday.--You are kidding .It --be him.He's gone back to
England .A couldn't B can't C mustn't D must
答
B .can't 表示推测的否定用can't,不可能couldn't 不行吗，我也选b,但答案是A ， 不解。表示推测的情态动词， 肯定用can , may, could, might, must, 否定用can't。 没见过用couldn't， 答案错了吧过去时态地时候不可以用couldn't 吗？你这句话不是对过去的推测