“特殊疑问词＋动词不定式”的用法
一、“疑问词+不定式”结构中。疑问代词who, what, which等和疑问副词when, where, how等后面跟不定式，以及连接副词whether与不定式连用构成不定式短语（这个不定时短语相当于一个名词）。这种结构在句中可作主语、宾语、表语、宾语的补语，状语，同位语等句子成分。注意：疑问副词why后不能跟动词不定式
作主语
Where to go is still a question. 到哪里去还是个问题。 （作主语，作主语时，谓语动词常用单数形式）
Choosing what to eat is no longer as easy as it once was.
选择吃什么,已经不像以前那么简单了。 作宾语
I know where to find the boy. 我知道到哪里能找到这个男孩。 （作动词know的宾语）
We must first solve the problem of whom to serve. 我们必须首先解决为谁服务的问题。（作介词of的宾语）
作表语
The question is how to learn English well. 问题是怎样学好英语。（作表语）
作宾语补语
I asked her how to learn English. 我问她如何学英语。 （用双宾语，宾语补足语）
做状语
She was at a loss what to do. 她不知如何是好。（做状语）
做同位语
The question whether to confess troubled the girl. 是否要坦白的问题使姑娘很烦恼。（做同位语）
I have no idea which one to take. 我不知道拿哪个好。（同位语）
二、“特殊疑问词＋动词不定式”结构经常用在某些动词后作宾语，类似的动词有：tell, show, know, learn, teach, find out, forget, wonder, remember等。如：
1，I’ll show you how to do it. 我要让你看看如何做这件事。, 2，You’d better find out where to put it. 你最好弄清楚要把它放在哪里。
作双重宾语（宾语补足语）：某些动词后面可接\＋疑问词＋不定式\构成的双重宾语，这类动词常用的有advise, ask, show, teach, tell等。例如：
He will advise you what to do. 他会建议你们做什么
Will you show me how to use this machine? 你能示范教我如何使用这部机器吗？
作介词宾语：某些介词后面可接\疑问词＋不定式\作宾语，这类介词常用的有 about, as, from, in, of, on, with等。例如：
You also need to learn the basic skills of rafting, such as how to handle the raft, how to paddle and how to get in and out of the raft. 你还需要学习基本划木筏的技巧，比如驾驭木筏的方法，划桨方法，上下木筏的方法。
He has no idea of how to answer this question.
他不知道怎样回答这个问题。
Della had only $1.87 with which to buy Jim a present.
德拉仅有$1.87为来吉姆买一件礼物。(which是关系代词) You have a number of topics from which to choose.
你有很多题目可以选择。(which是关系代词)
When you are trying to advise someone about what to do or what not to do, you can use should / ought to or should not /ought not to.
当你想要建议某人做什么或者不做什么时，你可以用should / ought to 或者 should not / ought not to。
三、“特殊疑问词＋动词不定式”这种结构可以把复合句转为简单句。如： 1，I don’t know what I’ll do next.
= I don’t know what to do next.
2，The doctor told him when he should take the medicine. = The doctor told him when to take the medicine.
同样，因为“特殊疑问词＋动词不定式”这种结构相当于一个名词性从句，所以可用同等成分的从句代替，从而把简单句转换为复合句。改写时只需在疑问词后加上适当的主语，并把不定式改为适当的形式的谓语即可。如： 1，Li Ping doesn’t know why to learn English. = Li Ping doesn’t know why he should learn English. 2，Which to choose is important.
= Which we should choose is important. 3，The question is where to go.
= The question is where we should go.
四、“特殊疑问词＋动词不定式”这种结构可构成独立问句。如： What to do? 怎么办？
How to get rid of the trouble? 如何摆脱困境？
然而，这个结构看似简单，但也容易出错，有几点是需要我们注意的：
易错一：
按照英语语法的习惯，疑问副词why后不直接跟动词不定式。如： 误：I don't know why to choose that dictionary. （X） 正：I don’t know why you must choose that dictionary.
但它可以接不带to的动词不定式（即动词原形），构成Why do sth.?/Why not do sth? 结构。肯定形式表示某动作是不必要的或没有意义的，而否定形式则用于向某人提建议和表达看法，相当于祈使句。
Today is Sunday. Why not go out to relax yourself? 今天是周日，干嘛不出去轻松一下呢？
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