祈使句用以表达命令,要求,请求,劝告等.
1） 祈使句有两种类型,一种是以动词原形开头,在动词原形之前加do (但只限于省略第二人称主语的句子).
Take this seat.
Do be careful.
否定结构：
Don't move.
Don't be late.
2） 第二种祈使句以let开头.
Let 的反意疑问句
a. Let's 包括说话者
Let's have another try,shall we / shan't we?
= Shall we have another try?
b. Let us 不包括说话者
Let us have another try,will you / won't you?
= Will you please let us have another try?
否定结构：
Let's not talk of that matter.
Let us not talk of that matter.
