祈使句

　　祈使句表示请求、命令、叮嘱、号召等，主语一般是you，在句子中省略，谓语动词用原形，否定一般在谓语前加don't .如：

　　Let's not waste time arguing about it. (waste time doing)

　　Be sure to come here before nine.

　　Don't do that again.

　　Don't hesitatie to turn to me if you are in trouble. (turn to sb.向某人求助)