学习是一个坚持不懈的过程，走走停停便难有成就。比如烧开水，在烧到80度是停下来，等水冷了又烧，没烧开又停，如此周而复始，又费精力又费电，很难喝到水。以下是小编给大家整理的高二英语选修三第二单元知识点，希望大家能够喜欢!
高二英语选修三第二单元知识点1
一、引导主语从句的连词主要有：
从属连词：that whether
连接代词：who whoever whom whose what whatever which whichever
连接副词：when where how why
二、用法
主语从句是在复合句中充当主语的从句，通常放在主句谓语动词之前或由形式主语it代替，而本身放在句子末尾。
1. It 作形式主语和it引导强调句的比较
①主语从句常用it作形式主语，一般常用句型为：It is+{名词/形容词/过去分词}+主语从句例如：
It is still a question whether she will come or not.
It is strange that you should like him.
It is still unknown which team will win the match.
另外，还有一些比较多见的结构：
It turned out that……;
It has been proved that……;
It happened/occurred that……;
It is well-known that……等等
②而强调句则不同，它的结构是：It+be+被强调部分+that+从句
强调主语：It is the times that produce their heroes.时势造英雄
强调宾语：It is English that Prof.Lin teaches us.
强调状语：It was in shanghai that I saw the film.
判断是否是强调句有一个方法，就是将that以后的“句子的其余部分”拿出来单独看，看有没有缺成分，缺的是什么成分，再把谓语动词后面that前面的那部分，带到你认为缺成分的地方，如果放进去是一句完整的句子了，那就说明是强调句。
2. 用it 作形式主语的结构
(1) It is +名词+that从句
It is a fact that … 事实是……
It is an honor that …非常荣幸
It is common knowledge that …是常识
(2) it is +形容词+that从句
It is natural that… 很自然……
It is strange that… 奇怪的是……
(3) it +不及物动词+that从句
It seems that… 似乎……
It happened that… 碰巧……
(4) it is+过去分词+that从句
It is reported that… 据报道……
It has been proved that… 已证实……
3.主语从句不可位于句首的五种情况
(1) if引导的主语从句不可居于复合句句首。
(2) It is said , (reported) …结构中的主语从句不可提前。例如：
It is said that President Jingo will visit our school next week.
(3) It happens…, It occurs… 结构中的主语从句不可提前。例如：
It occurred to him that he failed in the examination.
(4) It doesn’t matter how/whether …结构中的主语从句不可提前。例如：
It doesn’t matter whether he is wrong or not..
(5) 含主语从句的复合句是疑问句时，主语从句不可提前。例如：
Is it likely that it will rain in the evening?
4. What 与that 在引导主语从句时的区别
What 引导主语从句时在从句中充当句子成分，如主语.宾语.表语，而that 则不然。例如：
What you said yesterday is right.
三、宾语从句用以区分主语从句的几个特征
1、引导词：what which whose when whet herif where
2语序：宾语从句必须是用陈述语句。(名词性从句都是陈述语序)
如：I think that you must work harder.
宾语从句的引导词、连接词的区别、否定转移等现象。
补充：从句的语序永远是陈述句。
高二英语选修三第二单元知识点2
【First aid知识点】
1. first aid 的意思是“急救”，例如：first aid to the injured 给予伤员的急救。
短语联想：
give/offer aid 援助 come to sb's aid 帮助某人
teaching aids 教具 medical aid 医疗救护
with the aid of 借助于
get injured 受伤，在现代英语中大量地出现了由“get + 及物动词不达意的过去分词”构成的被动语态，这叫 get - 型被动语态。又如：
The computer got (was)damaged when we were moving. 我们搬家的时候，电脑碰坏了。
高二英语选修三第二单元知识点3
Worried about the journey, I was unsettled for the first few days.
Well-known for their expertise, his parents’ company …..
Confused by the new surroundings, I was hit by the lack of fresh air.
Exhausted, I slid into the bed and fell fast asleep.
过去分词作状语：过去分词作状语时，说明动作发生的背景或情况，其等同于一个状语从句。vt 过去分词作状语时与主句主语构成被动关系，表示被动和完成，vi 过去分词表示状态或动作的完成。
Heated , water changes into steam .
The professor came in, followed by a group of young people .
1 作原因状语，等于as / since / because 引导从句
Moved by what she said ,we couldn’t help crying . = ( As we are moved by what she said …
2 作时间状语，等于when 引导时间从句，如果分词表示的动作与谓语的动作同时发生，可在分词前加when/ while / until 等使时间意义更明确。
When heated , water can be changed into steam .
Seen from the hill ,the park looks very beautiful .= ( When the park is seen from the hill…
3 作条件状语等于 if / whether 引导从句
Given more attention , the cabbages could have grown better .= ( If they have been given more attention ….
Compared with you , we still have a long way to go = ( If we are compared with you
4 作方式或伴随状语
The actress came in , followed by her fans .
She sat by the window , lost in thought .
5 作让步状语
Much tired ,he still kept on working .=(Although he was tired ,) he ….
6 独立主格结构： 当分词的逻辑主语不是主句主语时，分词可以有自己独立的逻辑主语，这种结构称为独立主格结构。常用来表示伴随情况。
The boy rushed into the classroom , his face covered with sweat .
All things considered ,your article is of great value than hers .
Rewrite with proper conjunctions
Example : United we stand, divided we fall.
If we are united, we will stand, but if we are divided,we will fall.
1 Asked what had happened, he told us about it.
→When he was asked what had happened, …
2 Well known for his expert advice, he received many invitations to give lectures.
→Because he was well known for his expert advice, …
3 Given more time, we would be able to do the work much better.
If we were given more time,
4 Once translated into Chinese, the book became very popular among Chinese teenagers.
Once it was translated into Chinese,
5 Deeply interested in medicine, she decided to become a doctor.
Because she was deeply interested in medicine,
6 Left alone at home, Sam did not feel afraid at all.
Although he was left alone at home,
现在分词与过去分词作状语
现在分词作状语时，与其逻辑主语之间是主动关系，;而过去分词与其逻辑主语之间则表示被动关系。
Seeing these pictures, I couldn’t help thinking of those days when I was in Beijing . Seen from the top of a thirty-storeyed building, Beijing looks more magnificent. (see)
选择现在分词还是过去分词，关键看主句的主语。如分词的动作是主句的主语发出，分词就选用现在分词，反之就用过去分词。例如：
Used for a long time, the book looks old.
由于用了很长时间，这本书看上去很旧。
Using the book, I find it useful.
在使用的过程中，我发现这本书很有用
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