Look Mr Green is on the other side of the streetIt be him.He has gone to Londo

问题补充：

--- Look, Mr Green is on the other side of the street.

--- It be him.He has gone to London on business.

A. must

B. might not

C. can’t

D. mustn’t

答案：

A. must

B. might not

(答案→)C. can’t

D. mustn’t

解析：must必须，一定；might not可能不，比can’t语气较弱，表推测；can’t不能，表示客观本能上不能；mustn’t禁止。句意；看，格林先生在街的另一边。——不可能是他。他已经出差去伦敦了。故选C。