21. ----Did you know that Alice can speak three languages?

   ----______ ? I find that very hard to believe.

   A. Right            B. Sure            C. Really         D. Certainly

22. He takes no ______ in politics.

   A. interest          B. interested         C. interesting     D. interests

23. ----Is Jack on duty today?

   ----It _______ be him. It’s his turn tomorrow.

   A. mustn’t          B. won’t            C. can’t          D. needn’t