21.In recent years global warming has become concern for people all over the world.
---Would you like some more beef?---No, thanks. I’m ______ a diet.
At the wedding, he sang a song specially written for the ____.
----- Is that Mr.Smith over there? ----- No, it _____ be him --- I am sure he is much taller.
---Is it good to look up every new word when I come across it in reading? ---No. You ______because you are likely to guess the meaning from the context. A. can’t B. mustn’t C. don’t have to C. ought not to
—Shall we go out for ______ meal this evening? —Yes,that’s _____ good idea.