If在英语句中的位置和三种类型
一、句子成分：句子是有不同的各部分组成的，这些部分就叫做句子成分。句子成分可以是单词、词组或句子（从句）。在句中起主要作用的是主语、谓语，称为主要成分；起次要作用的有宾语、宾语补足语、定语、状语和表语，称为次要成分。所有的句子都是在简单句的基础上展开的，所以我们首先讨论简单句的五种基本句型。
一、简单句的五种基本句型(Five kinds of simple sentences)
（一） 主语 + 不及物动词（主、谓结构）
eg. 1）He is working.
2）He cooks.
（二） 主语+ 及物动词 + 宾语（主、谓、宾结构）
eg. 1）We study English every day.
2）They are playing football
（三） 主语+ 连系动词 + 表语（主、系、表结构）
eg. 1）Trees turn green.
2）He is happy.
常见的连系动词有：be ; become ; get（“天气”变得）; turn（“颜色”变得）; feel（觉得/摸起来）; look(看起来)；smell(闻起来); sound(听起来)；taste(尝起来)；seem(似乎).
特别注意：
a) 连系动词后常接形容词常作表语；
b) be / become后常接名词或相当于名词的短语（不定式/动名词）做表语。
c) seem + 形容词 = seem to be + 形容词
eg.1)He is a teacher (名词做表语)
2)His job is to feed animals (不定式做表语)
3)His hobby is reading. (动名词做表语)
4)He seems happy = He seems to be happy
（四） 主语 + 及物动词 + 间宾（人）+ 直宾（物）
=主语+ 及物动词 + 直宾（物）+ to / for + 间宾（人）
常用的此类动词有：give ; pass ; show ; lend ; buy. 但buy与for连用
eg.1)I gave him a book.
= I gave a book to him.
2)My mother bought me a pen yesterday.
= My mother bought a pen for me.
（五） 主语 + 及物动词 + 宾语 + 宾补
注意作宾补的词：1）名词（指宾语是谁/什么）；2）形容词；3）不定式；4）动词的ing 形式。
eg.1)We call him Jim.（名词做宾补）
2)We must keep the window open.（形容词做宾补）
3)The news makes me happy (同上)
4)I found it hard to get to sleep (同上)
5)I think it useful to learn English well (同上)
6)He told me to wash the plates.（不定式做宾补）
7)I saw a thief going into your room. （动名词做宾补）
特别注意：
1)动词不定式作宾补
A: ask / want / tell sb to do sth.
其否定式为：ask/want/tell sb not to do sth
2)省to不定式作宾补，即：
(l, m, n; 3h; 2看; 1f) sb do sth
l—let, m—make, n—notice; 3h—hear, have , help; 2看—see, watch; 1f—feel.
eg.1)The boss made the workers work 12 hours every day.
2)I often hear him sing.
2)区别省to不定式作宾补与动词ing形式作宾补.
hear / see sb do: 听见/看见某人做了某事
hear / see sb doing: 听见/看见某人在做某事
二、词类和句子成分的关系。
（一）词类相互间的关系。
1．形容词、数词通常修饰名词（有时名词也可以修饰另外一个名词），形容词还可修饰代词。例如：
1)The three tall and strong men are all basket-
(定语) (主) (谓) (定语)
ball players.（“主系表”结构）
(表语)
数词three和形容词tall , strong修饰名词men; 名词basketball修饰名词players.
2)The writer often writes something interesting
(主) (壮) (谓) (宾) (定)
about children. （“主胃宾”结构）
(定)
形容词interesting修饰不定代词something
2．副词常修饰动词、形容词和其他副词。例如：
(副词well修饰plays，副词quite修饰另一副词well.)
(副词very修饰形容词interesting)
以上的名词、代词、数词、形容词、动词、副词称为实词，可以在句中单独做一定的成分。
3．冠词、介词、连词称为虚词，在句中不能单独构成句子成分。冠词只能用于名词前；介词与它后面的名词或代词构成介词短语，才能作一定的成分（定语、状语和表语）。例如：
（介词短语of Class Two作定语，修饰the League members. 介词短语in the school yard作地点状语,修饰are having）
连词只起连接词、词组和句子的作用。
He is so young that he can’t go to school.
（that连接两句子）
（二）词类和句子成分的关系：
1．主语：是句子要说明的人和物，是句子的主体，一般放在句首。名词、代词常在句中作主语。此外，动名词、动词不定式、主语从句也可作主语。例如：
1)Mr. Chen is a greadt scientist. (名词作主语)
2)He reads newspapers every day. (代词作主)
3)Smoking is harmful to the health. (动名词作主语)
4)To swim in Kuming Lake is a great pleasure. (动词不定式作主语)
5)What we shall do next is not yet decided. (主语从句作主语)
2．谓语：说明主语的动作和状态。动词在句中作谓语，一般放在主语之后。例如：
1)The new term begins on September 1st .(行为动词作谓语)
2)She seems tired. (连系动词作谓语)
3)He has gone to Beijing. (行为动词作谓语)
3．宾语：及物动词涉及的人或物称为动词宾语。宾语一般放在及物动词（或相当于及物动词的短语）后。介词后的名词或代词称为介词宾语。名词、代词在句中常作宾语。此外，动词不定式、动名词和从句也可作宾语。例如：
1)Wang Ling lent me a novel. (代词me作间接宾语；名词a novel作直接宾语)
2)The medicine is good for a cough. ( 名词a cough作介词宾语)
3)My little sister always likes to ask questions. (不定式to ask questions作动词likes 的宾语)
4)His brother is good at playing chess. (动词名词playing chess作介词宾语)
5)Would you mind coming earlier tomorrow? (coming作动词宾语)
4．宾语补足语（复合宾语的第二部分）：在宾语后补充说明宾语的动作、状态、特征的成分称为宾补。名词、形容词、动词不定式和动名词可作宾补。（见前面简单句的五种基本句型五）
5．表语：在连系动词后用来说明主语的身份、状态或特征的成分是表语。可作表语的有：名词、代词、形容词、介词短语、不定式、动名词以及表语从句。（参见简单句的五种基本句型三）
1)Wang Lin’s father is a doctor. (名词a doctor作表语，说明主语的身份是doctor)
2)He is from America. （介词短语from America作表语，说明主语的特征是“来自美国“）
3)The baby is asleep. (形容词asleep作表语，说明主语的状态是“睡着的”)
4)His work is teaching English. (动名词短语teaching English作表语，说明主语特征是“教英语”)
5)This is why he was late for school(表语从句why he was late for school作表语。)
6．定语：用来修饰名词或代词的成分是定语。单词作定语通常放在它所修饰的词前；但修饰复合不定代词（nothing, anything, everything, something , somebody , anybody, …..）时，则放在这些不定代词之后。短语和从句作定语时，也放在被修饰词之后。形容词、名词、代词、数词、副词、介词短语、动词不定式、现在分词、过去分词和定语从句等都可作定语。
1)He is reading an interesting book. (形容词interesting作定语,修饰名词book)
2)I have something important to tell you. (形容词important以及不定式to tell you作定语，修饰不定代词something)
3)There are few women workers in the factory. (形容词few 以及名词women作定语修饰名词workers)
4)The oil workers here come from Daqing. (名词oil以及副词here作定语修饰名词workers)
5)We have got ten desks in the room. (数词ten修饰名词desks)
6)Yesterday the scientist made a report on modern science. （介词短语on modern science作定语修饰名词report.）
7)The girl playing the piano is my younger sister. (现在分词短语playing the piano作定语修饰名词girl)
8)This is the new dictionary which I bought yesterday. (定语从句which I bought yesterday作定语修饰名词dictionary)
7．状语：修饰动词、形容词、副词或全句的成分是状语。修饰形容词的状语通常放在它所修饰的词之前，修饰动词的状语通常放在动词后。但有些副词（如：often , always , usually等作状语放在事义动词之前，be /助/情之后）。副词、介词短语、名词词组、动词不定式、分词短语和状语从句都可以作状语。
1)He knows how to learn English well. (副词well作状语，修饰动词learn)
2)My parents often tell us about their hard life in the past. (副词often作状语，修饰动词tell)
3)Her mother usually goes out to do some shopping on Sundays. (副词usually以及介词短语on Sundays作状语，修饰动词goes)
4)He will leave for Shanghai the day after tomorrow. (名词词组the day after tomorrow作状语，修饰动词will leave)
5)He came here to see you. (动词不定式to see you作目的状语，
6)He sat there reading a novel (现在分词短语reading a novel作状语修饰动词sat)
7)If I have some free time, I will study German. (条件状语从句If I have some free time作状语)
三、用分析法确定一个单词在句中的词性和成分。
在英语中，一个单词往往有多种意思，应根据一个词在句中的位置确定它的词性、词义、和在句中的成分。
1)Excuse me. I don’t want to listen to you any more. I don’t think it’s a good excuse for being late for school
第一个excuse是动词“原谅”；第二个excuse有冠词a修饰，它是一个名词“借口”，在此作表语）
2)The scores are hard to believe. Team A has scored eight goals.
第一个score作主语，是一个名词“分数”；第二个score作谓语，是一个动词“进球”
3)The guide pointed to a red point on the map to show us where the tomb is.
第一个point作谓语，是一个动词“指着”；第二个point作动词pointed to 的宾语，在此是一个名词“（红）点”
4)When I felt some rain drops dropping on my face, I put on my raincoat.
第一个drop作动词felt的宾语，是一个名词“（雨）滴”；第二个drop是一个现在分词短语作宾语rain drops的宾语补足语，是一个动词“落下”
5)The sound from the church sounds very beautiful.
第一个sound作主语，是一个名词“声音”；第二个sound作谓语，是一个连系动词“听起来”。
6)She is a quiet girl. He does everything quietly.
第一处的quiet作定语修饰名词girl, 是一个形容词“安静的， 文静的”；第二处的quietly作状语修饰动词does, 是一个副词“安静地”
多给我点分吧！！！
1. to result in clinically meaningful outcomes for
This is the first study to show that writing can result in clinically meanful outcomes for chronicallyil-ill patients.
写作对...在临床方面会给病人带来有意义的结果
2. to cut back on medication
one of the key benefits of acupuncture is that it has few, if any, side-effects; and that when used with standard drug treatment-in anesthesia, for example---it allows physicians to cut back on medication, delivering the same level of benefit with fewer negative effects.
减少用药（量）
3. to trigger dangerous allergies in
in people, for example. Soybeans with genes added from brazil nuts to make them more nutritious, can trigger dangerous allergies in people allergic to brazil nuts.
来自巴西的大豆，为了提高其营养价值而进行过改基因，这会对一些对巴西坚果过敏的人引起危险的过敏反应。
4. to be summoned immediately to provide
他们立即应召提供...
get you the right treatment with the least delay
为你提供正确的治疗，将延误降至最低
Pre-hospital staff---paramedics, emergency medical technicians---through a sophisticated communication system know where and when the accident happened, and they are summoned immediately to provide the initial, quick, life-saving care. If you have a serious injury anywhere in Maryland, this system will get you the right treatment with the least delay.
5. to spring into action
该系统立即开始动作（或：该系统立即启动）
the system springs into action with a telephone call to 911, your local emergency number anywhere in the state.
6. to have a poor chance of
if he stays in shock, he has a poor chance of survival.
如果他仍然处于休克状态，他幸存的机会就极低。
7. to act as a clearing house for
Rifkin医生在接受美国ABC电视台采访时说，美国的医生在线对...就像是进行大清扫一样。
感觉应该是cleaning house，不是clearing house吧，在网上查了一下，没找到原文
Dr. Rifkin told ABC news that America’s Doctor Online acts as a clearing house for the hundreds of thousands of responses a web brouser might turn up in answer to a question.
8. to help set the standard for
帮助建立...的标准
I am very comfortable with what we’re doing. We want to help set the standard for this become it is coming.
9. bit and bites
点滴的，不完整的
But Cantra says their new technologies are not just about bits and bites.
10. to lay a foundation for/to provide a foundation for
为...打下（坚实的）基础
the royal Swedish academy of sciences, which awards them, says the new nobel physics laureates have laid a stable foundation for modern information technology. In addition, the discovery provides a foundation for the development of molecular computers.
11. to push information through
帮助信息通过互联网的光纤线路
The Swedish Academy is honoring them for their inventions of fast optical and microelectronic components found in compact disk players and bar code readers and which help push information through the interner’s optical fibers.
大致就帮你回答到此吧，看样子你在练习听力，祝你学习进步
It is not certain if / whether he will go abroad.
（置于句首时，只能用whether: Whether he will go abroad is not certain.)
I wonder if he knows it.
(介词后只能用whether: We are talking about whether we will go.)
2. if 引导条件状语从句, 该从句可置于主句前后:
If he goes, I won't go. = I won't go if he goes.
If I were a bird, I could fly in the sky.
3. if only用于感叹句:
If only I could fly. = I wish I could fly.
4. 用于if...or not:
I don't know if he will go or not.
= I don't know whether he will go or not.
= I don't know whether or not he will go.
5. 用于if so、if not:
If so, I will go. If not, I won't go.
6. 用于as if、even if:
He looks as if he knows it.
Even if he knows, he won't tell me.
①引导条件状语从句，译为如果
eg。if it rains tomorrow，I will not go to school。
（主句用一般将来时，从句一般现在时）
句首或句中
②引导宾语从句，译为是否
eg。I want to know if she will come
（主句一般现在时时，从句时态根据实际情况而定，主句过去时时，从句用相对应的过去某种时态）
仅仅句中
③even if引导让步状语从句，译为即使
eg。Even if he knows, he won't tell me.
句首
这可是一点点打下来的，给最佳吧
If 可置于句首或句中。下面进行论断说明：
1. if 引导名词从句，作主语、宾语：
It is not certain if / whether he will go abroad.
（置于句首时，只能用whether: Whether he will go abroad is not certain.)
I wonder if he knows it.
(介词后只能用whether: We are talking about whether we will go.)
2. if 引导条件状语从句, 该从句可置于主句前后:
If he goes, I won't go. = I won't go if he goes.
If I were a bird, I could fly in the sky.
3. if only用于感叹句:
If only I could fly. = I wish I could fly.
4. 用于if...or not:
I don't know if he will go or not.
= I don't know whether he will go or not.
= I don't know whether or not he will go.
5. 用于if so、if not:
If so, I will go. If not, I won't go.
6. 用于as if、even if:
He looks as if he knows it.
Even if he knows, he won't tell me.
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