祈使句的用法 Be型 (be+ 表语) Be quiet , please . 否定形式:Don't be late . Do 型 (实义动词+其他) Come here , please . 否定形式:Don't play football here . let型 (let sb. do sth. ) Let me have a try . 否定形式:Don't let sb. do sth. 或 Let sb. not do sth. 后者更常用 No 型 (No +n./ving) No photos. No smoking .