-Is Jack on duty today? -It be him; it's his turn tomorrow. A．mustn't B．won't C．

—Is Jack on duty today?

—It ________ be him; it's his turn tomorrow.

A．mustn't 

B．won't

C．can't 

D．needn't

试题答案

C解析：根据答语的后半句可知“一定不是他值日”，can表示推测时经常用于否定句或疑问句中。mustn't表示禁止，不能用来表示推测。