问题：
---Who ______ it be that hasn’t handed it in yesterday.
---It _______ be Bob. He handed it in yesterday.
A．can; mustn’t
B．must; can
C．can; can’t
D．may; mustn’t
---Who ______ it be that hasn’t handed it in yesterday.
---It _______ be Bob. He handed it in yesterday.
---It _______ be Bob. He handed it in yesterday.
| A．can; mustn’t | B．must; can | C．can; can’t | D．may; mustn’t |
参考答案：