（1）疑问词+不定式结构 BAG )
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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： ,;)Y 1q}Q
When to start has not been decided.何时动身尚未决定。（主语） _ui03veA1
I don't know what to do.我不知道该怎么办。（宾语） ^hzlR[
The difficulty was how to cross the river.困难在于如何过河。（表语） a
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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） 26PUO$&b.
（注）A.有时疑问词前可用介词，如： u~[HC)4(0
I have no idea of how to do it.我不知道如何做此事。 , (dg]7
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： GmP)"@O](;
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. h[ #Lg3
（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）。 <f.* =/]W2
When the streets are full of melting snow, you cannot help but getting your shoes wet. o(w!x!["
（3）不带to的不定式 n|2`y?
1）在表示生理感觉的动词后的不定式不带to。这类词有： s0uI;WMg
feel 觉得 observe 注意到，看到 overhear听到 XK??5'&{
watch注视 listen to听 perceive察觉，感知 4)0 % ^\p
notice注意 see看见 look at看 hear听 [zv>Wlf,%
On seeing the young child fell into the lake，Eric sprang to his feet，and went on the rescue. _;(`u!@/{
2）另一类是某些使役动词，如make, let，have等。如： /_<`#?5T(
Let him do it.让他做吧。 ~\kJir
I would have you know that I am ill.我想要你知道我病了。 kP~'C'5Ys
（注）： e 8g" QDc
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： `Fa49B|`D
He was seen to come. JYuI~<:
The boy was made to go to bed early. **_`AM~
②在动词find与help之后，不定式可带to亦可不带to，如： g?` g+:nug
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。 7?Q@Hj(:NT
3）在do nothing／anything／everything but（except）结构中。例如： y_EkW
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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。 H,,-;tN ?
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。 ALvj)I`Al
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。 d\aKGq;8C
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。 9rXbv4{
（4）不定式与动名词的逻辑主语和分词独立结构 x{4Rm,Dxn
1）不定式的逻辑主语为：for +名词（或代词宾格）+ 不定式。例如：
o&uO ]
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。 7pM l:\
（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： ?xEQ'(UBQ
It was wise of him to do that.他那样做是明智的。 f!6oW( r-L
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： hY
2nT
Tom insisted on my going with them.他坚持要我和他们一起去。 piYv }4;:(
He dislikes his wife's working late.他不喜欢他妻子工作得很晚。 F*V<L
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 }$M 2XF
It is very kind of you to help me.你帮助我太好了。 <;O=h;
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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）。 #o Rm-yDr
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。 z ogtIn)
