. -May we leave the classroom now?
-No, you ______. You ______ to leave until the bell rings.

. -May we leave the classroom now?
-No, you ______. You ______ to leave until the bell rings.

— Wow! You look different! You            wear glasses.
— Yes, I did. But now I am wearing contact lenses(隐形眼镜).

You______be tired after playing sports for a long time without a rest.
A.must                   B.need                 C.can’t

Trees ____ fight air pollution．They are natural air conditioners．

The red bike _______be Hu’s. She has a blue bike.

–Look at that girl! Is it Susan?
--No, it _______ be her. She has gone back to her hometown.

---Must I do the work today? 
---No, you _______. You may do it tomorrow.

You _______ see a dentist when you have a toothache. 

—Is Nancy knocking at the door?
—No, it ________ be Nancy. She has gone to Guangzhou.
A. can’t            B. mustn’t              C. won’t