B. 用法：
　　動詞不定式具有名詞、形容詞和副詞的特征。因此在句中可以做主語、表語、賓語、賓語補足語、定語和狀語。

　　一、不定式做主語：
　　1、不定式做主語一般表示具體的某次動作。===動名詞doing 表示習慣的，經常的動作。
　　e.g: To finish the building in a month is difficult.
　　To do such things is foolish.
　　To see is to believe. (對等)
　　注: 1). 不定式作主語時,謂語用單數
　　2). 當主語較長，謂語較短時，常用it做形式主語，而將不定式放到謂語的后面。
　　it做形式主語，不定式放在謂語動詞之后常用于下列結構中：
　　(1)It is/was +adj.+of sb. to do…
　　(2) It is +adj.+for sb.+to do…
　　It is easy / difficult / hard / foolish / unwise / right / wrong / unnecessary
　　(3) it is +a +名詞+ to do...
　　It is a pity / a pleasure / a pleasant thing / one’s duty / an honor / a shame / a crime / no easy job… to do
　　It takes (sb.) some time / courage / patience …to do… 
　　It requires courage / patience / hard work… to do…
　　*注意: probable 和 possible 均可作表語，但possible可以用不定式作真實主語， 而probable不能用不定式作真實主語。
　　It is probable for him to come to the meeting.(錯）
　　It is possible for him to come to the meeting.
　　It is possible / probable that he will come to the meeting.

　　二、不定式做表語
　　主語是以aim duty hope idea intention plan job suggestion wish purpose task 等為中心詞的名詞詞組 或以 what 引導的名詞性從句表示，后面的不定式說明其內容, 不定式作表語常表示將來或現在的動作或狀態。
　　eg My idea is to climb the mountain from the north.
　　Your mistake was not to write that letter.
　　What I would suggest is to start work at once.

　　三 動詞不定式作賓語
　　以不定式結構為賓語的動詞有：
　　ask, agree, care, choose, demand, decide, expect, fail, help, hope, learn, manage, offer, plan, prepare, pretend, promise, refuse, want, wish等只能用動詞不定式作賓語
　　口訣（接不定式作賓語的動詞）
　　想要學習 早打算（ want learn plan）
　　快準備 有希望（ prepare hope wish expect）
　　同意否 供選擇（agree offer choose） 
　　決定了 已答應（decide be determined promise）
　　盡力去 著手做（manage undertake）
　　別拒絕 別假裝（refuse pretend）
　　失敗不是屬于你（fail）
　　e.g.Tom refused to lend me his pen.
　　We hope to get there before dark.
　　The girl decided to do it herself.
　　*注意:某些及物動詞可用-ing也可用動詞不定式作賓語但意義不同的有
　　stop go on remember forget
　　regret try mean can’t help
　　be used to

　　四． 動詞不定式做定語
　　1．. 不定式作定語需要后置。
　　2. 作定語的不定式與被修飾的名詞或代詞存在著兩種主要的邏輯關系，即被修飾的名詞和代詞是不定式的邏輯主語 （邏輯上的主謂關系）或邏輯賓語（邏輯上的動賓關系）
　　1）不定式前的名詞是它的邏輯主語。
　　He is the doctor to do the operation.
　　2) 不定式和它所修飾的名詞是邏輯上的動賓關系。
　　I have a lot of things to do. 
　　3）不定式前的名詞是它修飾的對象。
　　This is the right time to start.
　　注意．如果不定式所修飾的詞是way 或 place, 介詞可省略。
　　He has no way to go (by). This is the best place to work (at)

　　五．賓語補足語
　　He want you to be his assistant. I saw her cross the street.
　　[注1] 如果謂語動詞為感官動詞或使役動詞，則作賓補的不定式不可帶to，這些動詞有see, hear, feel, watch, notice; have, make, let等。
　　I felt my blood run cold. What made you think like that?
　　但如果句子是被動語態，則to不可省略。
　　He was made to clean the windows as a punishment.
　　Someone was heard to come up the stairs.
　　[注2] 1.謂語動詞help后可接帶to或不帶to的不定式作賓補。用不帶to的不定式表示幫助者直接參與動作；用帶to的不定式表示主語沒有直接參與動作。
　　They helped me carry the boxes.
　　This kind of soap will help you to wash the clothes more easily.
　　2.在美式英語或非正式文體中，help后用作賓補的不定式均不帶to。
　　3.help后可以直接用帶to或不帶to的不定式作賓語。
　　They helped (to) carry the furniture upstairs. 
　　[注3]look at及listen to后用作賓補的不定式不帶to（這主要是美式英語）。
　　We have been listening to the radio tell a long story.

　　六 ．表語補足語 當不定式與主語存在邏輯上動賓關系的時候，用主動表被動。
　　That is hard to say. The chair is comfortable to sit in.

　　七． 不定式做狀語
　　不定式做狀語修飾動詞、形容詞、副詞等，表示目的、原因、結果、 條件等。
　　1、表目的 e.g. To learn a foreign language well, you must try your best (主語一致)
　　He came here to attend an important meeting.　　　
　　He came here in order to see Charlie.
　　I turned the radio down so as not to disturb him
　　注：表示目的的不定式可以置于句首，這也是區別于 其他功能的標志之一。
　　* 但是，置于句首表示目的的不定式可以是to, in order to ，但卻不可以是so as to. ”,” To draw maps properly, you need a special pen.
　　In order to draw maps properly, you need a special pen.
　　To get the best results, use clean water.
　　To be elected monitor of our class, he gave money to us.
　　* 放在句末時， to do 表示目的， 不可有“，”若有用doing 表示伴隨的目的
　　e.g. He bowed to us to thank us for helping him find the way.
　　He worked day and night, hoping to finish the work beforehand.
　　注：1. 不定式結構表示目的時，通常句子的主語就是它的邏輯主語 (主語一致)
　　e.g.He bought a bicycle to go to town more quickly.
　　He went home to see his mother. 
　　例外 e g He opened the door for the children to come in.
　　They sent a man to mend the window.
　　2、表結果
　　不定式結構表示結果更常見于下列句型
　　① so …as to …
　　Would you be so kind as to lend me your bicycle / tell me the time?
　　② such (…) as to …
　　I’m not such a fool as to believe that.
　　③ adj./adv. + enough to …
　　The boy is old enough to go to school.
　　④ too … to …
　　His eyesight is too poor to read such small letters.
　　（5）only to find , only to be told 出乎意料之外的結果
　　3． 原因不定式可以用于動詞、形容詞或-ed分詞后表示原因。
　　He was too excited to get high marks.

　　八．同位語
　　Is this your purpose, to avoid being punished?

　　九．獨立成分
　　To tell you the truth, I don’t like you. They arrived here at 11:55 a.m., to be exact.
　　類似的有：to be frank坦率地說，to hear him talk聽他說話的口氣，to cut a long story short 長話短說，等等。