—Is Jack on duty today?—It be him. It’s his turn tomorrow. A. mustn’tB. won’tC. can’tD.

问题补充：

—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

答案：

A. mustn’t

B. won’t

(答案→)C. can’t

D. needn’t

解析：根据下文的It’s his turn tomorrow可知，Jack今天“不可能”(can’t)当班，故应选C。