It's nearly seven o'clock.Jack __ be here at any moment

问题描述:

It's nearly seven o'clock.Jack __ be here at any moment
A must
B need
C should
D can
我只想问一下,A怎么不行了?

这是初中的题目吧.很明显选C表推测,因为JACK来不来还不确定,所以不选A