--Look! It ________ be Jack on the playground.

--It ________ be him. Because I saw him enter the school library just now.

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

-Look! It __________ be Jack on the playground.

-It ______ be him. Because I saw him enter the school library just now.

A. can; must     B. can; cant    C. may; mustn′t     D. must; can′t