How do you look after your goldfish?—They need clean water, and remember not to _____ with your hands.

There is _______ interesting book on the teacher’s desk.–Oh, ______ book is Wei Fang’s.

________ climb the mountains（山）.

Now the air in our city is ________ than it used to be．Something must be done to stop it．

Hey, Jack. You ________ on the phone just now. But you weren’t here and the man left a phone number. —Oh? I was in the library.