------Is this ruler Mary’s?------No it Mary’s. Hers is on the desk..A. can beB. can’t beC

问题补充：

------Is this ruler Mary’s?

------No, it Mary’s. Hers is on the desk..

A. can be

B. can’t be

C. must be

D. mustn’t be

答案：

A. can be

(答案→)B. can’t be

C. must be

D. mustn’t be

解析：否定性推测要用can’t。