e.g: To finish the building in a month is difficult.
To do such things is foolish.
To see is to believe. （对等）
注: 1）. 不定式作主语时，谓语用单数
（1）It is/was +adj.+of sb. to do…
（2） It is +adj.+for sb.+to do…
It is easy / difficult / hard / foolish / unwise / right / wrong / unnecessary
（3） it is +a +名词+ to do...
It is a pity / a pleasure / a pleasant thing / one’s duty / an honor / a shame / a crime / no easy job… to do
It takes （sb.） some time / courage / patience …to do…
It requires courage / patience / hard work… to do…
_注意: probable 和 possible 均可作表语，但possible可以用不定式作真实主语， 而probable不能用不定式作真实主语。
It is probable for him to come to the meeting.（错）
It is possible for him to come to the meeting.
It is possible / probable that he will come to the meeting.
主语是以aim duty hope idea intention plan job suggestion wish purpose task 等为中心词的名词词组 或以 what 引导的名词性从句表示，后面的不定式说明其内容， 不定式作表语常表示将来或现在的动作或状态。
eg :My idea is to climb the mountain from the north.
Your mistake was not to write that letter.
What I would suggest is to start work at once.
ask， agree， care， choose， demand， decide， expect， fail， help， hope， learn， manage， offer， plan， prepare， pretend， promise， refuse， want， wish等只能用动词不定式作宾语
想要学习 早打算（ want learn plan）
快准备 有希望（ prepare hope wish expect）
同意否 供选择（agree offer choose）
决定了 已答应（decide be determined promise）
尽力去 着手做（manage undertake）
别拒绝 别假装（refuse pretend）
e.g.Tom refused to lend me his pen.
We hope to get there before dark.
The girl decided to do it herself.
1. defend against保卫…以免受
2.intruduce sb tosb 向某人介绍某人
3.kiss sb on somepart亲吻某人的某个部位
4.in defence 防御，保障
5.together with 与某人一起
6.be likely to 很可能…；有希望…
7.reach one’s hand out to sth 把手伸出来取某物
8.on the contrary 相反
9.nod at sb 向某人点头
10.greet sbwith/by 通过…向某人问候
11.express one’s feelings表达某人的感情
12. in general 总的来说；通常
13.at a job fair 在求职会上
14.be nervousabout 对…感到紧张
15. at ease 舒适；快活；自由自在
16. lose face丢脸
17.turn one’s back to 背对；背弃
18.turn one’s head away 把头转过去
19.be willing to 渴望…. ， 愿意….
20. look upsetabout sth 对.. 感到沮丧
1. I saw several young people enter thewaiting area looking around curiously.
2. The firstperson to arrive was Tony Garcia from Colombia， closely followed by Julia Smithfrom Britain.第一个到达的是从哥伦比亚来的托尼•加西亚，随后紧跟着的是英国的茱莉亚•史密斯。
3. She steppedback appearing surprised and put up her hands， as if in defense.
4. Not allcultures greet each other the same way， Nor are they comfortable in the sameway with
touching ordistance between people.
5. We can often bewrong about each other， so it is an amazing thing that we understand each otheras well as we do.
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
The actress came in ， followed by her fans .
She sat by the window ， lost in thought .
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，
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）
Used for a long time， the book looks old.
Using the book， I find it useful.
_____ in thought， he almost ran into the car in front of him. （ lose）
______ in white， she looks more beautiful.（ dress）
be lost in
be dressed in
be interested in
be devoted to
be supposed to? be caught in the rain
be seated in
be prepared for
be determined to
generally speaking 一般说来
strictly/ frankly speaking 严格地说/坦白地说
judging from 从…判断
all things considered 从整体来看
taking all things into consideration 全面看来
例如：Judging from his face， he must be ill.从他的脸色看，他一定是病了。
Generally speaking， dogs can run faster than pigs.
总的来说，狗比猪跑得快。 （speaking 不是dogs 的动作）
1. Complete each sentences using the P.P. of the right verb.
build frighten trap follow shoot see examine
1 ________ by noises in the night， the girl no longer dared to sleep in her room.
2 The lady returned home， ________ by two policemen.
3 After having been _________ carefully， the room was locked again.
4.______ in 1949， the exhibition hall is over 50 years old.
5 _____ from a distance， the Opera House looks like ship sails.
6 If _____ in a burning building， you should send for help.
7 Although ______ in the leg， he continued firing at the police.