The river will be dirtier and dirtier________we do nothing to protect them.
—Do you know the man _______ is talking with our English teacher? —Oh, he must be Lin Tao's father. He was looking for Lin Tao just now.
---What should we do to fight A/H1N1 flu? ---We should wash hands often, avoid ______ to crowded places and so on.
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.