13.1 祈使句結(jié)構(gòu)
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  祈使句用以表達(dá)命令,要求,請(qǐng)求,勸告等。

1) 祈使句有兩種類型,一種是以動(dòng)詞原形開頭,在動(dòng)詞原形之前加do (但只限于省略第二人稱主語的句子)。
    Take this seat.
    Do be careful.
 否定結(jié)構(gòu):
   Don't move.
   Don't be late.

2) 第二種祈使句以let開頭。
  Let 的反意疑問句
 a. Let's 包括說話者 
   Let's have another try,shall we / shan't we?
  = Shall we have another try?

 b. Let us 不包括說話者
   Let us have another try,will you / won't you?
  = Will you please let us have another try?

否定結(jié)構(gòu):
 Let's not talk of that matter.
 Let us not talk of that matter.