用所给词的正确形式填空。
【小题1】He _________ (have to) stay at home because it is raining outside.
【小题2】Kitty, please don’t _________ (play) with fire!
【小题3】The paper is _________ (make) from wood.
【小题4】The tree in front of my house _________ (keep) the air clean.