1. 肯定形式：动词原形● e.g. Stay in bed for a couple of days. 卧床休息几天。
● e.g. Remember to switch off all the lights. 记得把所有的灯关掉。
2. 否定形式①：Don't+动词原形● e.g. Don't eat in the classroom. 别在教室里吃东西。● e.g. Don't run in the street. 别在大街上乱跑。
3. 否定形式②：Never+动词原形● e.g. Never answer the phone while driving. 不要在开车的时候接电话。
