从句往往是很多学生的难点，碰到从句的题时，很多学生就头疼。其实很多时候不是学生不会做这类题，而是他们没有掌握做此类题的方法。那怎样才能快速地做这样一类题呢？我个人认为，有以下几点：
要能快速而准确地断句
当学生们碰到一个难长句的时候，很多学生一下子就懵了，不知道从哪着手。其实第一步就是要找出句子的主干，明白句子的中心意思。这样才能把主句和从句分开。比如：
Anyone who cares about what schools and colleges teach and how their students learn will be interested in the memoir (回忆录) of Ralph W. Tyler, who is one of the most famous men in American education.
我们来分析句子的结构：这是一个复合句。首先找出句子的主干：Anyone will be interested in the memoir。Anyone是主语，谓语是will be interested in，memoir是宾语。
Anyone后面是一个由who引导的定语从句，用来限定Anyone所指的范围。在这个从句中，又包含两个由and连接并分别由what和how 引导的宾语从句，表示cares about的内容。
判断从句所属类型
我们已经把主句和从句分开了，现在要做的就是判断一下从句到底是什么从句。
英语中存在三类从句：定语从句、状语从句和名词性从句。
判断的方法在于：看从句在整个句子中充当什么成分。充当定语就是定语从句，充当状语就是状语从句，充当主语就是主语从句。在这一步骤中又存在一些方法：
一般来说，只要使用在名词或代词后面的从句都是定语从句；
放在介词和动词后面的都是宾语从句；
句中有it做形式主语或形式宾语的话，那么后面的从句就是主语或宾语从句；
放在系动词和一些相当于系动词的词（remain, get, turn）后面的都是表语从句；
放在一些抽象名词后面的且在从句中不充当成分的都是同位语从句。比如：
It is by no means clear _____the president can do to end the strike.
句子的主干就是it is by no means，显然在这个句中it充当的是形式主语，后面的_____the president can do就是一个主语从句，这是从句中缺少主语，我们就填的是what.
A lot of language learning, _____ has been discovered, is happening in the first year of life, so parents should talk much to their children during the period.
句子的主干就是language learning is happening in the first year of life. _____ has been discovered用来修饰整个主句的内容，又放在主句的中间，所以这是一个非限制性定语从句修饰整个主句的内容。我们都知道在定语从句中内代替整个句子内容的有两个引导词：which和as，只有as在引导非限制性定语从句时能放在句中，所以这个地方填的就是as。
________he is, he will be thinking of you.
显然这句话的主干就是：he will be thinking of you. _____ he is在整个句子当中充当的就是状语，所以这部分就是状语从句。在这个状语从句中缺乏的就是表语，想到众多的引导词以后，我们最终选择了wherever。因为wherever的意思是“无论在哪”，刚好符合题意，所以是最合适的一个。
Is this desk____ he bought for me yesterday?
Is this the desk _____ he bought for me yesterday?
碰到一般疑问句了，怎么办呢？我们第一步就是要把它变成陈述句。所以第一句话的主干就是this desk is…,第二句话的主干就是this is the desk。很显然，第一句话后面的从句he bought for me就是一个表语从句，而第二句话后面的从句he bought for me就是一个定语从句。在第一句话中，表语从句中缺乏宾语，所以填的就是what。在第二句话中，定语从句中缺的也是宾语，我们填的是which/that或不填。所以做题时一定要细致，向这两个题的区别就在于一个定冠词the.
判断从句中缺什么成分
判断从句中缺什么成分，然后根据各种从句的规则选择引导词。值得注意的有：
（1）在定语从句中，除了as之外的引导词，其他词都没有实在意义。还有就是定语从句中的引导词不包括what, how和-ever型的词，在状语从句中的引导词不包括that。在名词性从句和状语从句中，除了要判断出从句中所缺成分之外，还要把引导词的意思带进句中，这样才能最终选择出答案。
（2）关于that在各从句中的作用。我们都知道that在定语从句中指人或物，在从句中充当主语、宾语或表语。而that在名词性从句中则不充当任何成分，也没有实在意义。
（3）关于no matter+疑问词和-ever型的疑问词的适用范围。no matter+疑问词只能引导状语从句，而和-ever型的疑问词既可引导名词性从句，又可引导状语从句。
（4）在定语从句中，如果引导词后面紧跟了一个名词，那么引导词一定填的是whose，此时的whose可以和of which/whom +名词或者是the+名词+of which/whom互换。
(5)在定语从句中缺的成分只有主宾表或状语。如果在判断完句子都不缺主要成分的情况下，那肯定就是缺状语。要注意一些特殊的先行词在句中充当状语时，用的是引导词where。比如：position, occasion, condition, stage等。请分析下面的句子：
①Sorry I’m late, but you cannot imagine ______ trouble I took to find your house.
②—Why didn’t you chat with that friendly foreigner just now?
-- I’d like to have, but the trouble was _____ he said was difficult for me to understand.
③She’ll never forget her stay there _____ she found her son who had gone missing two years before.
④“I’d like to give my thanks to those _____ help my son will be able to survive his terrible disease.” Said the mother on TV.
⑤Some people are worried about the year 2012 _____ they think the earth will end in disaster,
Keys: what; that what; when; with whose; when.
下面请大家分析一下的难长句，找出句子的主干以及分析句中的其他成分。
1. This will be particularly true since energy pinch will make it difficult to continue agriculture in the high-energy American fashion that makes it possible to combine few farmers with high yields.
结构分析:句子的主干是This will be particularly true…。since引导原因状语从句。此从句中又套嵌一个由关系代词that引导的定语从句，修饰the high-energy American fashion。在定语从句中，that做主语，makes做谓语，it做形式宾语，不定式短语to combine few farmers with high yields则是真正的宾语（不定式短语内部to combine是主干，few farmers是宾语，with high yields是状语），possible做宾语补足语。this指代前句中提到的这种困境。energy pinch译为“能源的匮乏”;in…fashion译为“用…方法、方式”。
2. Now since the assessment of intelligence is a comparative matter，we must be sure that the scale with which we are comparing our subjects provides a“valid”or“fair”comparison.
结构分析:句子的主干是we must be sure…。since引导原因状语从句the assessment of intelligence is a comparative matter。主句中又有that引导的宾语从句that the scale with which we are comparing our subjects provides a“valid”or“fair”comparison。此宾语从句中又套嵌一个由介词with+which引导的定语从句with which we are comparing our subjects修饰先行词the scale。scale在此处意为“尺度、衡量标准”。
3. In general，the tests work most effectively when the qualities to be measured can be most precisely defined and least effectively when what is to be measured or predicted can be not well defined.
结构分析:句子的框架是the tests work most effectively when…and least effectively when…。and连接两个并列分句，每个并列分句中皆有一个when引导的时间状语从句分别说明work most effectively和and（work）least effectively。第二个时间状语从句中还有一个主语从句what…predicted。the tests是主句的主语，work为动词做谓语。qualities在此处是可数名词，不译为“质量”，而译为“特征”。defined不能直译为“被定义为”，而应译为主动语态“界定”。
4. For example，they do not compensate for gross social inequality，and thus do not tell how able an underprivileged youngster might have been had he grown up under more favorable circumstances.
结构分析:句子的框架是they do not compensate…，and thus do not tell how…。and连接两个并列分句，第二个并列分句中由how引导的宾语从句是一个带有虚拟条件句的主从复合句，其中had he grown up…（=If he had grown up…）是省略了连词if的非真实条件句。主句主语的they，在此代指上文提到的tests; able在句中作might have been的表语。underprivileged在此不能译为“没有特权的”，而译为“没有地位的”或“物质条件差的”。
5.It leads the discussion to extremes at the outset：it invites you to think that animals should be treated either with the consideration humans extend to other humans，or with no consideration at all.
结构分析:句子的框架是It leads the discussion to extremes at the outset: it invites you to think that…。冒号后的复合句是对冒号前部分作进一步说明。复合句中that引导宾语从句，从句中有either…or…引导的两个并列的介词结构作状语，修饰动词be treated，其中第一个with介词结构中还有一个省略了关系代词that或which的定语从句humans extend to other humans，修饰the consideration。it代指上文的观点，即如果对人权没有达成一致看法，而谈论动物的权利是徒劳的。介词短语at the outset译为“从一开始”。动词invites应转译为“使”、“让”或“促使”。动宾结构extend consideration to意为“给予关怀或关心”，consideration不应译为“考虑”。
6. But even more important，it was the farthest that scientists had been able to look into the past，for what they were seeing were the patterns and structures that existed 15 billion years ago.
结构分析:句子的框架是it was the farthest that…。但It was…that…在本句中不是强调句型。it是指上句中所提到的150亿年前形成的巨大云团（a strip of enormous cosmic clouds some 15 billion light-years from earth）;that引导的应是一个定语从句，修饰先行词the farthest。for引导的是表示原因的分句，分句中还有that引导的定语从句，修饰the patterns and structure。
7. Thus it happened that when the new factories that were springing up required labor，tens of thousands of homeless and hungry agricultural workers，with their wives and children，were forced into the cities in search of work，and any work，under any condition，that would keep them alive.
结构分析:句子的框架是it happened that…。it做形式主语，that引导的从句做真正的主语。主语从句中，又有一个由when引导的时间状语从句，主句为tens of thousands of homeless and hungry agricultural workers…were forced…，时间状语从句中从句主语the new factories又带有一个定语从句that were springing up; that would keep them alive做work的定语从句。spring up意为“发生，出现，建立”。
8. As a result of two or three centuries of scientific investigation we have come to believe that nature is understandable in the sense that when we ask her questions by way of appropriate observations and experiments，she will answer truly and reward us with discoveries that endure.
结构分析:句子的框架是…we have come to believe that…。that引导的从句做believe的宾语从句;此从句中有一个that从句作the sense的同位语从句;同位语从句中又套嵌一个由when引导的时间状语从句;此时间状语从句又套嵌一个定语从句that endure，修饰其先行词discoveries。by way of意为“经由，通过…方法”;reward sb. with意为“以…报答，酬劳”;endure此处应译为“持久，持续”,不要译为“忍受，容忍”。
9. These new observational capabilities would result in simply a mass of details were it not for the fact that theoretical understanding has reached the stage at which it is becoming possible to indicate the kind of measurements required for reliable weather forecasting.
结构分析:句子的框架是These new observational capabilities would result in simply a mass of details…。后面紧跟省略了if引导的虚拟条件句were it not for the fact that…，即if it were not for the fact that…;that从句作the fact的同位语从句。此从句中又套嵌一个定语从句，修饰其先行词the stage; required for reliable weather forecasting为过去分词短语修饰the kind of measurements。simply译为“只不过，仅仅”，不应译为“简单地”。
10. The story of the discovery of what is now generally called the principle of Archimedes，namely that a solid body when immersed in a liquid loses a portion of its weight of the liquid it displaces，has many different versions，of which the following is one.
结构分析:句子的框架是The story…has many different versions…。what is now generally called the principle of Archimedes为名词性从句做介词of的宾语。namely that a solid body…作the principle of Archimedes的同位语;when immersed in a liquid是省略了主语的过去分词短语，句子补充完整为when the solid body is immersed in a liquid，修饰其主句a solid body loses a portion of its weight of the liquid…;it displaces是省略了关系代词that的定语从句修饰the liquid，it代指前面提到的the solid body;同时，of which the following is one又构成先行词versions的定语从句。displace意为“排（水）”;version不译为“版本”，此处指“根据个人观点的（对事件等的）说法，看法”;句尾的one代指a version。