一、“疑问词＋不定式”结构中的疑问词,包括疑问代词who,what,which和疑问副词how,when,where等.这些疑问词和不定式一起构成了不定式短语,这种结构可在句子中作主语、宾语、表语等.例如：
①How to do it is aquestion．该怎样做倒是一个问题.（作主语）
②I really don't know what to write about．我实在不知道该写些什么.（作动词宾语）
③We must first solve the problem of whom to serve．我们必须首先解决为谁服务的问题.（作介词宾语）
④The question is where to put it．问题是该把它放在哪儿才好.（作表语）
⑤I asked him how to learn English．我问他如何学习英语.（作宾语补足语）
二、“疑问词＋不定式”结构相当于一个名词性从句,常常可用同等成分的从句代替.改写时只需在疑问词后加一适当主语,并将不定式改成适当形式的谓语.上述例句可以分别改写成：
①How we should do it is a question．
②I really don't know what I should write about．
③We mustfirst solve the problem ofwhom we should serve．
④The question is where we should put it．
⑤I asked him how we should learn English．
三、“疑问词＋不定式”结构经常放在tell,show,teach,learn,know,wonder,discuss,re- member,forget,find out等动词（词组）之后作宾语.例如：
The teacher told the students how to do the experiment．老师教学生如何做实验.（句中 told含有taught的意思）
The young woman doesn't know what to do．那位年轻女子不知道怎么办.（句中what不能改换成how）
He tells me how to answer all the questions in English．他告诉我怎样用英语回答所有的问题.（句中的how不能省去）
另外,这种结构可以构成独立问句.例如：What to do?怎么办?
How to get rid of the trouble?如何摆脱困境?
巩固练习：
I．用“疑问词＋不定式”改写下列句子.
①How we should do it was discussed last night．
____ was discussed last night．
②I didn't know where I should go．
I didn't know ____ ．
③The difficulty was how we should cross the river．
The difficulty was ____ ．
II．根据汉语补全下列英语译文.
①何时动身还不知道.
____ is unknown．
②我忘了该怎么办.
I forgot ____ ．
③我可以告诉你哪里可以买到此书.
I can tell you ____ ．
Keys：I．① How to do it②where to go ③ how to cross the river
II．①When to start②what to do③ Where to buy（get）this book
