—Look! A book is on the floor. Whose is it?—It be Rick’s. It has his name on it.A. mustn’

问题补充：

—Look! A book is on the floor. Whose is it?

—It be Rick’s. It has his name on it.

A. mustn’t

B. can’t

C. must

D. need

答案：

A. mustn’t

B. can’t

(答案→)C. must

D. need

解析：mustn’t一定不，禁止；can’t不可能；must 必须，一定；need需要。句意：看，地板上有本书。是谁的？——一定是瑞克的。上面有他的名字。结合语境可知选C。