三类从句。
名词性从句：
nominative/noun clauses
1. 主语从句 subject clause
除基础知识外，另外要掌握的：
a. 识别it作形式主语，主语从句后置。
it is a privilege that you h**e invited me to the party.
b. whether, if引导主语从句的区别。
c. whatever, whoever, whenever , wherever引导主语从句时，不可以用no matter what/who/when/where替换。在引导让步状语从句时，可互换。
2. 宾语从句 object clause
a. 识别it作形式宾语， 宾语从句后置。
i consider it an honor that you h**e invited me to your wedding.
b. whether, if引导的宾语从句可互换(没有和or not连用时)，但介词后的宾语从句只能用whether, 不能用if.
it is a question of whether we should compromise our integrity.
c. 不可省略连词that的5种情况可浏览一下，有个印象：两个以上宾语从句，有插入语，直宾， that从句后置，宾语从句是复合句，且复合句中从句位于主句之前。
3. 表语从句 predicative clause
a. 位于系动词之后；
b. 可用whether, as if, as though引导。
it looks as if it is going to rain.
c. 当主句的主语是reason时，引导词用that, 不能用because.
the reason why they were upset was that they lost the game.
4. 同位语从句 appositive clause;
1. 通常在抽象名词之后，连词that 通常不可省略；if不能引导同位语从句；
we are not looking into the question whether he is worth trusting. (if不对)
2. 和定语从句的区别： 作句子成分？
3. doubt在否定句中带同位语从句时的引导词是that, 在肯定句中一般用whether.
i don’t doubt __he can finish the task on time.
i doubt __they can swim across the river.
定语从句 attributive clause:
先行词：antecedent
关系代词：relative pronoun
限定性 restrictive ~，非限定性 non restrictive ~
1. 关系代词that, who, which用法区分；
2. 只能用 that的情况：先行词前有特定的修饰词，不定代词；先行词是人+物的时候；
3. 关系代词 which前可加介词，that前不能加介词；
4. as, which引导非限制性定语从句的区别。
5. 定语从句中的谓语动词和先行词保持一致：
he is one of the players who are awarded a prize.
he is the only one of the players who is awarded a prize.
状语从句 adverbial clause：
时间 ~ of time，地点 ~ of place，原因 ~ of cause，比较 ~ of comparison，结果 ~ of result，条件 ~ of condition，让步 ~ of concession，目的 ~ of purpose，
1. for fear that, lest引导的目的状语从句要用should do/be:
she put an extra blanket over the baby lest/for fear that he should catch a cold.
2. as, though引导的让步状语从句；as要倒装，though可倒装，也可不倒装。
3. though, although让步状语从句中，主句可用yet, still, 但不能用but.
though he is rich, yet/still he is unhappy.
3. while可引导让步，通常放句首。
4. not…because否定because引导的原因状语从句。
the mountain is not famous because it is high.
5. a is b as/what c is d.比较状语从句。
各类表示比较的结构： comparisons
a. as...as…: as good as dead /sold (实际上等于，与…一样)
b. more/less…than…: 与其…不如…
this book seems to be more a dictionary than a grammar book.
c. no less a than b: a和b一样。
a whale is no less a mammal than a horse is.
d. no more…than b, not…any more than b：同b一样不…
one minute too late is no more in time than half an hour is.
e. more than: 多于，非常，不只是。
her performance is more than good; it was perfect.
f. not so much a as b: 与其说…不如说。
the high-tech company ceo is not so much a computer expert as a sharp businessman.
g. not so much as：甚至不，连…都不…
i h**e not so much as heard of him, much less know him.
真题练习。状语从句： adverbial clause
1you __further problems with your printer, contact your dealer for advice. (2005)
a. if, had b. h**e, had
c. should, h**e
d. in case, had
答案：c。should位置提前到句首，表示与将来相反的可能性。a选项是虚拟语气；a, d选项时态错误。
2. nine is to three __three is to one. (2008)
a. when b. that
c. which d. what
答案：d。a is to b what c is to d是固定句式。
reading is to the mind what food is to the body.
3. men differ from animals __they can think and speak. (2008)
a. for which b. for that
c. in that d. in which
答案：c。in that意为“因为”，引导原因状语从句。a和d用来引导定语从句。
4. _he wanted to go out with his friends at the weekend, he had to stay behind to finish his assignment. (2008)
a. much though
b. much as
c. as much
d. though much
答案：b。much as意为“尽管”，相当于though和although，引导让步状语从句，故选b。as much意为“同样地”。
5. i enjoyed myself so much __i visited my friends in paris last year. (2008)
a. when b. which
c. thatd. where
答案：a。本句没有出现先行词，可知这句话不是定语从句，后半句last year，故选when，引导时间状语从句。
6. _the boss says, it is unreasonable to ask me to work overtime without pay.（2009）
a. whatever b. whenever
c. whichever d. however
答案：a。whatever=no matter what，引导让步状语从句，表示“无论什么”，充当宾语；whenever引导时间状语从句，表示“无论何时”，与句意不符；whichever通常指一种选择关系，表示“无论哪个，无论哪些”；however引导让步状语从句时，后面常接形容词或副词。
7. fool __jerry is, he could not h**e done such a thing.（2010）
a. whob. as
c. liked. that
答案：b。as引导让步状语从句时，从句部分必须倒装，被倒装的部分可以是表语、状语或动词原形。
8. which of the following contains an adverbial clause of cause? (2012)
got a job as soon as i left university.
b. as there was no answer, i wrote again.
c. you must do the exercises as i show you.
d. wealthy as he is，mark is not a happy man.
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