Don’t _________ the bus until it has stopped. Safety is first.
The doctor did what he could_________ the dying man.
---Where does John live?---He lives on ______ floor but he doesn’t use a lift to go up and down.
—What bad weather!—Yes. If it _______raining, the fields will be covered with water soon.
-I wonder ____________. -Zebras.
-Why didn’t you go to the cinema with us this afternoon, Jim?-Because I ______ at the station for my uncle from Beijing at that time.