2 Let’s go to the zoo! 我们去动物园吧
(一)、由let带头的祈使句是个常见的动词句型,它的主要用法有下列三种：
1）表示“建议”。
这个句型里的let后头紧跟着一个第一人称的代词宾语,如：
Let me try.
Let's do it.
Let me go and look for it.
这个句型语气委婉,比直接的祈使句客气。试比较a、b两句：
a. Don't disturb him.
b. Let's not disturb him.
a是直接命令,语气强烈,不如b温柔悦耳。
2）表示“间接命令”或“愿望”。
这句型里的动词宾语是第三人称名词或代词,如：
Let Robert take charge of the marketing department.
Let her join our choir.
3）表示“警告”、“蔑视”、“威胁”等。
这种祈使句里的宾语也是以第三人称为主。除了口气凶悍之外,有时还语带讽刺,如：
Let him try and he will expose his inability to work on his own.
Let the invaders come and our armed forces will wipe them out in no time.
（二）、用“let”的祈使句时,必须注意下列几点：
1）let的否定句有二。如果宾语是第三人称用“Don't let...”；如果宾语是第一人称,则用“Let......not ”。如：
Don't let this type of things happen again.
It's raining now. Let's not go out until after the rain。
2）let只适用于现在时态,可以有被动语态 (the passive voice)。如：
Let the recalcitrant criminals be sent to prison.
Let all the dedicated capable staff be promoted.
3）let后头除了是不带“t”o的不定式动词之外,还可以是某些适当的副词,如out, in, down, alone等。如：
Let the puppy out.
Open the windows and let the fresh air in.
The room is too sunny. Let the blinds down.
Let me alone, please.
4）用“Let's”时,把谈话者的对象包括在内；用“Let us”时,并不包括对方。如：
Let's try it, shall we?
Let us do it by ourselves, will you?
