一、定语从句
引导定语从句的关系代词有that、which、who（宾格whom）、所有格whose和关系副词 where、when、why等。
关系代词或关系副词在定语从句中充当一个成分，关系代词that、which、who、whom等在从句中分别作主语或宾语，whose在从句中作定语，而关系副词when、where、why等在从句中作状语。
【举例】
I will never forget the days when/in which we worked together.
【解析】在句中，表示时间的名词the days在从句中充当的是状语，所以用关系副词when来代指，引导定语从句修饰先行词the days。
表示地点或原因的名词如果在从句中作状语，则用关系副词where 或why来代指；如果在从句中作动词的宾语，则用which或that来代替。
【举例】
①This is the factory where/in which I worked.（作状语）
②This is the factory that/which I visited years ago.（作宾语）
注：当先行词为time, reason, place时，引导词可以省略。
【举例】
This was the first (when/what) I had serious trouble with my boss. That is the reason (why) I did it. This is the place (where) we met yesterday.
另外，定语从句中谓语动词的数应与先行词的数相一致。
【举例】
①Mr. Jackson is the only foreigner that is present at the party.
②He is one of the students who were praised by the teacher.
【解析】在句①中，先行词foreigner被only修饰，强调只有一个，所以从句中谓语动词用单数形式。而在句②中，who引导的定语从句修饰先行词the students，为复数，所以从句谓语动词应为复数。
二、名词性从句中的易错点
1. that引导的定语从句与同位语从句
定语从句与前面的的名词是修饰与被修饰的关系，“……的名词”，而同位语从句是用来说明前面名词的内容。与that从句同位的名词必须是一些表示事实或概念的抽象名词。
【举例】
fact,news,belief,truth,reply等。That在定语从句中必须作成分，可用which或who/whom代替，而that在同位语从句中不充当任何句子成分，只起连接作用。
【举例】
Along with the letter was his promise that he would visit me this coming Christmas. Do you still remember the chicken farm that we visited three months ago.
【解析】在句①中，that引导同位语从句解释说明promise的内容，that不充当任何句子成分，只起连接作用，而在句②中，that在其引导的定语从句中作动词visited的宾语，对先行词the chicken farm起修饰作用。
2. 名词性从句中，关于it作形式主语和形式宾语的易错点
(1)名词性从句作主语或宾语时，为保持句子平衡，常用it作形式主语或形式宾语。
【举例】It’s a pity that he don’t come to give a speech.（形式主语）
We think it possible that you can finish the job today.（形式宾语）
(2)谓语动词 appreciate, dislike, hate, like, love, make等接由if或when 引导的宾语从句时往往在从句前加上形式宾语it。
【举例】I would appreciate it if you could come to my birthday party.
(3)动词take, hide, punish, put等,后接由that 引导的宾语从句，往往在从句前加形式宾语it。
【举例】I take it that you will be leaving Shanghai soon.
we punished it that we had finished the project ahead of time.
(4)短语动词answer for, count on， depend on, insist on, see to等后接有that引导的宾语从句时，必须冠以形式宾语it。
【举例】 I’m counting on it that you will come.
She’ll see to it that he goes ahead. 注：作形式主语和形式宾语时只能用it。
三、代词it,one,that的区别
one泛指，指代前面提到的那类人或物，用于指代可数名词，相当于a+名词单数，其复数形式ones前一般要有定语，否则就要用some。
that（those复数）即可指代不可数名词，表特指，相当于the+名词，后面经常与介词修饰语连用。It指代上文出现的名词，表示同类同物，另外还可表示时间、距离、天气,还可指代人称代词，表示性别身份不明，可作形式主语，形式宾语，引导强调句式以及一些固定搭配，如：get it, catch it, make it。
【举例】
① I have lost my watch. I think I must buy one.我丢了只表，我想我必须再买一只。（代指上文指到的同类事物，但不指同一个）
② Where is my pen Have you seen it 我的钢笔不知弄到哪去了，你见了吗？（代指上文提到的同一事物）
③ The land of China is larger than that of America.
④ Tom has a red pen and a blue one. （或two blue ones）
⑤ He has no child, and he wants to adopt one. （或 some）
四、反意疑问句中的易错点
1. 在一般疑问句中，无论肯定的问或是否定的问，如果回答为肯定则用yes，反之则用no。特别注意如果出现省略则看下文所暗示的意义。
① ―Are you a new comer
―Yes, I came here only yesterday.
② ―Isn’t Tom a good student
―Yes, he is excellent.
③―Don’t you think the composition good
―No, It can’t be any worse.
注意：在②③句中，当回答的意思与问句相一致时，则用No，译为“是的”，当回答的意思与问句相反时，则用Yes，译为“不” 。
2. 情态动词must
(1)I must leave now, mustn’t I
(2)He must be in the classroom, isn’t （表推测）
(3)He must have finished his homework, hasn’t he （表现在的结果）
He must have finished his homework yesterday afternoon,didn’t he （表过去）
当句子中有表示猜测的情态动词时，其反意疑问句的构成不能再用原句中的情态动词，而应根据原句在去掉情态动词的情况下的主谓关系来确定其反问形式。
五、非谓语动词中的易错点
非谓语与其逻辑主语（即动作的执行者或承受者）之间有三种关系，如为 主谓关系，则用现在分词或不定式的主动式；如为 被动关系则用过去分词、现在分词的被动（强调动作正在进行）或不定式的被动式（动作将进行）；如既无主动也无被动关系则只能用 状语从句或独立主格结构（即非谓语加上自己的逻辑主语）
Judging/considering/genrally speaking/supposing 指说话者的动作，故只用主动式。如：
Having been ill in bed for nearly a month, he had a hard time passing the exam.
解析：从这个句子可以看出，句词的逻辑主语与句子的主语he一致，并且是主谓关系，所以用了现在的分词作状语，同时，分词的动作明显地发生在句子的谓语动词动作之前，故采用了现代分词的完成式。
In order to improve English,( )
A.Jenny’s father bought her a lot of tapes.
B.Jenny’s father bought a lot of tapes for herself.
C.A lot of tapes were bought by Jenny.
D.A lot of tapes were bought by Jenny father.
解析：根据不定式短语我们可以推知，句子的逻辑主语应该是人而不是物，所以，应该排除CD，再就是应该是Jenny提高自己的英语，而不是她爸爸，故答案先B.
( )，we decided to go out for a walk.
A.It is fine B. It fine
C.Being fine D.It being fine
解析：主句主语we与动词短语be fine之间既无主动关系与无被动关系，所以要加上自己的逻辑主语It，由于不存在主、被动关系，故不能选C项，而应该选D 项。
( ) more attention, the trees could have grown better.
A. Given B.To give C.Giving D. Having giving
解析：give与主句的主语之间是被动关系，故选A，如为主动关系则选C。