名词，代词，名词化了的动词，形容词，分词，副词，数词，动词不定式或不定式短语， 从句，某些固定词组。例：she would be good for the job.她干这工作很合适。
名词作主语
例：the villagers didn't realize how serious the pollution was until the fish in the river died. 直到河里的鱼死了，村民们才意识到污染的严重性
s（subject主语）+ v（verb谓语动词） +o（object宾语）. 主系表结构 :s（subject主语）+v（verb谓语动词，也称为系动词，就是所说的“系”）
倒装：not until the fish in the river died did the villagers realize how serious the pollution was.
注意：倒装在主句，从句不倒装 /did 和not 提前，只剩动词原形
强调：it was not until the fish died in the river that the villagers realized how serious the pollution was.
如果强调的是主语或宾语且指人用who，其他一律用that。是that，而非其他/主句的顺序（倒装不强调，强调就不倒装）
人称代词（主格），名词性代词，指示代词，不定代词，such（----样的人、物），it（时间，天气，距离等）
at midnight /in the(泛指）middle of the night
例：it is 9 o'clock when i went home.
我回家的时候已经九点了
一般句：it was nine when i got home.
强调句：it was at nine that i got home.
原形：i got home at nine.
注意：作主语在句首/it作主语构成（常用 v-ing，不常用只有 use，good）
（1）it is +adj. +of sb.(人的属性）/for sb.（物的属性）to do
例：it is necessary to finish the design before national day. tomorrow is national day.
有必要在国庆节之前完成设计。明天是国庆日
（2）it is +n.+for/of sb. to do
例：it is not good manners for arabs to stand close talking to their friends.
对阿拉伯人来说，和他们的朋友说话离得近不是一个好习惯
在感叹句中必须用it作形式主语：what a joy/ pleasure (it is) to read the book.
在问句中必须用形式主语：is it possible to go to the moon by spaceship?：可以乘宇宙飞船去月球吗？
数词作主语
ten out of 100 americans are over /above /more than 65.
动名词作主语
一般 / 完成时
v-ing: 主动/doing/having done
not doing:被动/being done/having been done
注意：doing 无时间限定/与谓语同时出现/在谓语动词后发生having done发生在谓语之前
he still remembers being prized.
当逻辑主语为无生命的东西时
1.作主语时，通常表示一般性的无时间性的东西。而不定式表示某一种具体的动作。
smoking is habit difficult to break：抽烟的习惯很难打破的
2.主语和表语一致
seeing is believing：眼见为实
3.逻辑主语必须是所有格形式
the old man's taking pity on the snake leads to his death.那个老人怜悯那条蛇，导致他的死亡。
4.“it” 作形式主语：当表语为 no use，no good，no harm，any good，fun等名词或useless，nice，good，interesting，worthwhile等形容词时，句首常用it作形式主语，动名词后置。句型常用于说明“某种活动或某件事情如何”
不定式作主语
to +动词原形
not to do 解释：具有动词的性质，作宾语，状语/具有名词的性质，作主语/具有形容词性质，作定语/具有副词的性质，作状语。除谓语不可作之外，其他都可。
一般式：to do
进行时：to be doing
完成时：to have done
完成进行时：to have been doing
to do:表示动作发生在谓语之后，i want to go home.与谓语动词几乎同时发生
to be doing :表示与谓语动词同时发生
to have done:发生在谓语动词之前 someone was considered to have done something.
to have been doing :动作从过去开始一直持续到谓语动词这个动作的发生
不定式表示一种确定的动作 to do morning exercises this morning is not good for your health：今天早上去做早操对你的健康不好
名词化的形容词：the poor /the sick
名词化的过去分词：the disabled
名词化的介词短语：from my home to school is three kilometers：从我家到学校有三公里
副词----不定式或动名词
what an excitement to find a shark when you’re swimming in the sea. 当你在大海中游泳时，发现鲨鱼是多么兴奋的事
句子作主语
1）that引导的从句，无意义，不担当句子成分，不省略
a. it +v+ that从句
b. it +系动词+表语+that 从句
c. it is strange that he didn't come here yesterday：奇怪的是，昨天他没来这里
当形容词为important necessary strange /that should +动词原形
it is strange that he should （表示吃惊）pass the exam：奇怪的是，他可以通过考试
2）it is +n +that 从句
what a pity it is that you didn't come to this party：真遗憾你没来这个聚会
当名词为a pity/a shame /a surprise +should +v原形（表示竟然）
what a pity that she should be fail in exam：真遗憾，她竟然考试不及格
3） it is +过去分词+that 从句
it is reported that a car accident happened there：据报道，发生一场车祸
从句s +be v-ed + inf.
he is said to be studying in the usa：据说他在美国学习
有人建议suggest/order/request + 从句 should +动词原形
4） it +动词原形seem/appear /turn out/+that
it seems that it will rain：看来要下雨
it strikes sb. that 从句 ：表示“某人突然想…”
it occurs to sb. that从句：表示“某人发生了…”