There are no lights on and no one answer the doorbell. They( ) be at home

题目

There are no lights on and no one answer the doorbell. They( ) be at home
选择
并说明选它的理由
a.must not b.will not c. should not d.can not

答案

d
must表肯定猜测,否定是表猜测要用CAN'T