只有表示一时的行为的形容词才可用于be / don’t be之后，如careful / careless, patient / impatient, quiet, silly等(be / don’t be通常不可与指状态的形容词连用，如 hungry / thirsty, pretty)。
如：Be quiet! 安静点!Don’t be silly! 不要发傻!Do be patient. 一定要有耐心。Be careful about what you say. 说话要小心。Be more careful with your work. 你的工作要再细心一些。 careful not to break anything. 当心别打破什么了。Be sure you don’t break any of them. 千万别把它们打破了。Be sure to write to ma as soon as you get there. 到了千万给我来信。Be sure and come as soon as possible. 一定要尽快来。Be sure to send out all the invitations today. 一定要在今天把请帖都发出去。
