If I ______ free tomorrow, we ________to Beijing Zoo.

When shall we start?—-Let’s ______ it 8:30.Is that all right?

_________ do you go to the library? —I usually go to the library twice a week. [ ]

There are many apples ______the tree.[ ]

Air quality in our city is becoming worse and worse.—Yes. These days’ PM2.5 readings are frightening. We must do something to ______air pollution.