（1）疑问词+不定式结构
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疑问词who，what，which，when，where和how后加不定式可构成一种特殊的不定式短语。它在句中可以用作主语、宾语、表语和双重宾语。如： @x+2b0 b
When to start has not been decided.何时动身尚未决定。（主语） qJrKt=CE
I don't know what to do.我不知道该怎么办。（宾语） CssE8p >"F
The difficulty was how to cross the river.困难在于如何过河。（表语） BDWbWA
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I can tell you where to get this book.我可以告诉你哪里可以买到此书。（双重宾语） _3yG<'f[
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（注）A.有时疑问词前可用介词，如： 3U+FXK#6
I have no idea of how to do it.我不知道如何做此事。 ~Ss, he]Er
B.动词know 后面不能直接跟不定式作宾语，只能跟疑问词（如：how, what）+不定式： *Z_4bR4Q
While still a young boy, Tom knew to play the piano well and as he grew older, he wrote operas, the most famous of which is Carmen. y7fy9jQ
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（2）介词except和but作“只有…，只能…”讲时跟不定式结构（but与不带to的不定式连用）。 %}VH5s9\
When the streets are full of melting snow, you cannot help but getting your shoes wet. &t AYF_}
（3）不带to的不定式 cS9 jGD9
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1）在表示生理感觉的动词后的不定式不带to。这类词有： T TN!$?G3
feel 觉得 observe 注意到，看到 overhear听到 4$pV;xV
watch注视 listen to听 perceive察觉，感知 > ]^ 'h
notice注意 see看见 look at看 hear听 hyf
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On seeing the young child fell into the lake，Eric sprang to his feet，and went on the rescue. >- \bLr
2）另一类是某些使役动词，如make, let，have等。如： X$ ZV Y2
Let him do it.让他做吧。 4v hz `1
I would have you know that I am ill.我想要你知道我病了。 Y -a
（注）： Wq1 jT IQ
①上述感觉动词与使役动词转换为被动结构时。其后的不定式一般需带to，如： "
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He was seen to come. k Y~4AH
The boy was made to go to bed early. R; c9)>8L
②在动词find与help之后，不定式可带to亦可不带to，如： lbBWOx/|
He was surprised to find the sheep （to） break fence at this season.他发现羊在此季节越出栅栏，感到惊讶。 M>]A! W=
3）在do nothing／anything／everything but（except）结构中。例如： nm,LKS7
Last night I did nothing but watch TV.昨天晚上，我除了看电视别的什么也没有干。 <]M. K3>
但是，如果谓语动词不是“do nothing，anything，everything”，那么but（except）所跟的不定式则仍须带。 VE|l;aXi
The doctor told him nothing but to stop smoking.医生除了让他戒烟，其它什么都没有说。 5o d T\>Sn
There was nothing for them to do but to remain silent.除了保持沉默以外，他们没有别有别的办法。 $ItjVc@U
（4）不定式与动名词的逻辑主语和分词独立结构 Q,&Li+u|
1）不定式的逻辑主语为：for +名词（或代词宾格）+ 不定式。例如： 0B]q /G(
I found it impossible for him to do the job alone.我发现他—个人干这活是不可能的。
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（注）在表示人物性格、特性等的形容词后面，常用of引出不定式的逻辑主语。例如： d}[cX9U/
It was wise of him to do that.他那样做是明智的。 EJ9hgE
2）动名词的逻辑主语为；①人称代词的所有格+动名词；②名词‘s+动名词。例如： &xQM !f
Tom insisted on my going with them.他坚持要我和他们一起去。 :pqUUZ6x&
He dislikes his wife's working late.他不喜欢他妻子工作得很晚。 6 4zOEjra
3）某些形容词，如：careless等不定式后可以加of来引导出其逻辑主语。这类词主要有：absurd, bold, brave, courageous, careful, careless, clever, wise, foolish, silly, stupid, good, nice, kind thoughtful, considerate, greedy, generous, honest, modest, polite, rude, cruel ,selfish, wicked, wrong等 W-=6:y#A
It is very kind of you to help me.你帮助我太好了。 h^yqrDyJ
间或也可用for + there to be表示（而且there后面的不定式只能是to be）。 P2-&Im`+
It's a great pity for there to be much trouble in the company.太遗憾了公司里有这么多的麻烦。 $Iwvecn?I
