Question

---Look! A book is on the floor. Whose is it?
---It ______be Rick's. It has his name on it.

1. A.
   mustn't
2. B.
   can't
3. C.
   must
4. D.
   need

Answer 1

C
考查情态动词的用法。mustn’t“禁止；不要”；can’t“不可能”；must“一定”；need“必要”。由下文句意“在上面有他的名字”可知，这本书一定是里克的。故选C。