—Where is Bob? I cannot find him anywhere.
—He have been off long. I heard him make a call just now.
A. shouldn’t
B. can’t
C. mustn’t
D. needn’t
网友回答
A. shouldn’t
(答案→)B. can’t
C. mustn’t
D. needn’t
解析：考查情态动词与虚拟语气用法。语境表示语气很肯定的否定判断推测：我刚才还听见他打电话了，因此他一定没走多远。用can’t have done。