4)“whword＋不定式”结构不定式前加一个疑问代词(what,which, who, whom, whose)或疑问副词(where, when, how, why)，
常见的可以接这种不定式短语的动词有：know, see, decide, tell,ask,consider,discover,explain,findout,forget,guess,hear,imagine,inquire, learn,observe,perceive,remember,think,understand,wonder等。
I couldn’t decide which book to choose. I can tell youswheresto get this book.They found it hard to decide whether to go swimming next Sunday or to visit Aunt Sally in New Year.“whword+不定式”结构除了作宾语外，还可以在句中作主语或者表语。
When to start the program remains undecided. The question is how to put the plansintospractice.
a)不定式作状语表示目的。或用于so as和in order之后，来强调这种目的。
To learn a foreign language well, you must make painstaking efforts. Mother saved every cent she could spare to pay for my schooling. We must develop science and technology at high speed so as to raise scientific and cultural level of our country.
Insgroups to get a high mark in Band 4, he did a lot of exercises both in grammar and reading comprehension.
b)不定式表示结果，特别是在so...as to, such...as to, only to...以及too...to等结构中的不定式表示结果。
I rushed to the station as fast as I could, only to find the train already gone. She left her hometown with her beloved man, never to return. No one is too old to learn. Would you be so kind as to carry the luggage for me?
c)不定式常用来修饰形容词，构成下列词组：be able to,be afraid to, be apt to, be bound to, be certain to,be easy to, be eager to, be fit to, be likely to, be ready to, be sure to, be unable to, be unwilling to, be willing to等。
Chinese team is bound to win the World Cup.
It is likely to rain today, for it is very cloudy.
I am willing to help you with your homework, for we are friends.
ask, advise, allow, beg, cause, compel, command, enable,encourage, expect, feel, force, find, hear, have,inform, invite,let, make, mean, notice, order, permit, persuade,remind, require, request, teach, tell, urge, watch,warn, watch等。
Because of the complexity of the modern equipments,most offices require secretaries to have specified training.
He asked you to call him at ten o’clock.
The note reminds me to be careful whatever I do.
I’d never allow my children to behave like that.
当不定式在let, make, have, hear, look at, listen to, feel, observe, watch, notice, perceive(感觉到)等动词后面作宾语补语时， 不定式不带to.
Whenever something is wrong with you,please do let me know.
I will have the students write a passage about Internet.
I saw my mother shed tears at the news that the neighbor girl got seriously hurt in a car accident.
It seemed so long before he heard the stone hit the water.
原来的宾语变为主语，宾补则变为主补。加主补的动词主要有：assume, believe, know, report, say, suppose等。
Mr. Brown is said to have left for Italy last week.
(It is said that Mr. Brown left for Italy last week.)
Persons have been said to climb on roofs, solve mathematical problems, compose music, walk through windows and commit murder in their sleep.
He is reported to have won the 100meter running race in the Olympic games.
不定式常作下列的名词定语：attempt, ability, anything,chance, desire, determination, decision, effort, failure,intention, need, opportunity, plan, promise, pressure,right, tendency,time, way等。
His efforts to carry out the plan were successful.I have no intention to go to the cinema with you.
There is no need to bother him with such trifles.
There is a tendency to writer quite long sentences in commercial correspondence.
The pressure( )causes Americans to be energetic, but it also put them under a constant emotional strain.
A) to compete B) competing C) to be competed D)shavingscompeted
She is a very nice person to work with.
This is an important issue to talk about.
b)由only, last, next,序数词或形容词最高级修饰的名词常用不定式作定语。
Mr. Zhang is always the first man to arrive at the office and the last man to leave.I don’t think he is the best one to do the work.
9)不带to的不定式在下列词组后面的不定式不带to：would rather ...than(宁愿……也不), had better...(最好)，can’t help but...(不得不), had rather...(宁愿)，cannot but... (不得不，必然)，may/might as well...(不妨)，let alone(更不用说)。
【例如】 You’d better return the books to the library on time. Otherwise, you will be fined. I can’t help but wish that nothing would go wrong. They had never seen such delicious food, let alone eat it.