祈使句表示請求、命令、建議、邀請等，謂語動詞一律用原型，句子中通常
不用主語，句末用驚嘆好或者句號，用降調。

    ★肯定句：動詞原型

    Come here ， please. Go downstairs， please. Stand up. Sit down. Be
quiet. Be careful.

    祈使句中如果有喚語，一定要用逗號隔開，放在句首或者句尾：Come in ，
Amy. Sit down here， Tom. Mary， give me a book please.

    ★否定：Don't+動詞原型

    Don't come here. Don't sit down. Don't stand up. Don't give me it.

    let sb. do讓某人做

    Let me pass. Let us have a rest. Let's have a rest.

    反意疑問：Let's have a walk along the river ， shall we ？

    Let us go out for a drink ， will you ？