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却是一个高频词，活跃于英语书籍报刊文中的字里行间。It貌似小而简单,
1. it表示时间等
it用作“虚意”主语，本身没有具体的意义，常常出现于表示气候、天气、温度、时间、距离、地点、金钱等意义的句子里。例如：
When winter comes，it gets colder and colder in Northern China.
It seemed quite a long time before my turn came.
It is an 8-minute walk to the nearest mall from our company.
2.it
在it充当形式主语的句式里，it所处的位置在先(被称之为“先行”)，其后才出现正真的主语。真正的主语常常以动词不定式结构，-ing分词结构和名词性从句等形式出现。例如：
It is not wise for parents to give their children whatever they want.
It was pleasant meeting you and your girlfriend in Paris last month.
It is said that Professor Wang has come back from West Africa.
3.it
与it充当形式主语一样，
The newly-developed medicine makes it possible to treat the terrible disease: Ebola.
Our English teacher thinks it no good learning Grammar without practicing it.
The newly-elected president made it clear that he wanted his country to strengthen cultural exchanges with all the neighboring countries.
3. it
it作有实际意义的代词，可以指代下列情况：前文中提及的事物或内容；性别不明的小孩或者未知的人；未指明但谈话人都知道的那件事等。例如：
Yesterday the lady living next to me gave a birth to a baby and it was pretty lovely.
While his mother keeps telling him not to waste much time in playing computer games, it doesn’t work.
The doctor has gave me a second life. Never shall I forget it.(it指代句中未指明但谈话双方都知道的那件事：The doctor has gave me a second life)
4. it
it用在强调句式里，其通常的结构是：It+ be+
Was it because Jack came late for work that the boss got angry?
It was his father that/who helped you much last year.
It is this novel that I take a great interest in；that is why I have read it for forty times.
5. it与表示爱憎之类动词连用
it与表示爱憎、喜好等情感色彩的动词连用，构成一种特别的结构。能用于此结构的动词有appreciate, dislike，enjoy，hate, like, love, prefer。此外，动词短语depend on, rely on, see to等也适合于这一结构。此结构的表现形式为：sb + verb/ + it + if/when…和sb + verb phrase + it + that…。it用来指代从句里所提及的事情。例如：
I would appreciate it if you can help me look after my grandma when I am not at home.如果在我外出时你能帮我照顾我的奶奶的话,
The little girl dislikes it when her mother scolds her in public.
You may depend on it that your father will help you with your French.
6. it用在if和when引导的结构里
在if/when引导的结构里，it没有实际上的意义。此类结构的表现形式一般是：when it comes to…，if it comes to that
When it comes to the Chinese culture including classical Chinese nobody knows more than
I don’t really trust him — nor his wife, if it comes to that.
If it is convenient to you, I want to ask you to help me repair the roof of the kitchen next weekend.
7. it用在that/this is和think sb. is句式里
That is it, This is it
1. it表示时间等
it用作“虚意”主语，本身没有具体的意义，常常出现于表示气候、天气、温度、时间、距离、地点、金钱等意义的句子里。例如：
When winter comes，it gets colder and colder in Northern China.
It seemed quite a long time before my turn came.
It is an 8-minute walk to the nearest mall from our company.
2.it
在it充当形式主语的句式里，it所处的位置在先(被称之为“先行”)，其后才出现正真的主语。真正的主语常常以动词不定式结构，-ing分词结构和名词性从句等形式出现。例如：
It is not wise for parents to give their children whatever they want.
It was pleasant meeting you and your girlfriend in Paris last month.
It is said that Professor Wang has come back from West Africa.
3.it
与it充当形式主语一样，
The newly-developed medicine makes it possible to treat the terrible disease: Ebola.
Our English teacher thinks it no good learning Grammar without practicing it.
The newly-elected president made it clear that he wanted his country to strengthen cultural exchanges with all the neighboring countries.
3. it
it作有实际意义的代词，可以指代下列情况：前文中提及的事物或内容；性别不明的小孩或者未知的人；未指明但谈话人都知道的那件事等。例如：
Yesterday the lady living next to me gave a birth to a baby and it was pretty lovely.
While his mother keeps telling him not to waste much time in playing computer games, it doesn’t work.
The doctor has gave me a second life. Never shall I forget it.(it指代句中未指明但谈话双方都知道的那件事：The doctor has gave me a second life)
4. it
it用在强调句式里，其通常的结构是：It+ be+
Was it because Jack came late for work that the boss got angry?
It was his father that/who helped you much last year.
It is this novel that I take a great interest in；that is why I have read it for forty times.
5. it与表示爱憎之类动词连用
it与表示爱憎、喜好等情感色彩的动词连用，构成一种特别的结构。能用于此结构的动词有appreciate, dislike，enjoy，hate, like, love, prefer。此外，动词短语depend on, rely on, see to等也适合于这一结构。此结构的表现形式为：sb + verb/ + it + if/when…和sb + verb phrase + it + that…。it用来指代从句里所提及的事情。例如：
I would appreciate it if you can help me look after my grandma when I am not at home.如果在我外出时你能帮我照顾我的奶奶的话,
The little girl dislikes it when her mother scolds her in public.
You may depend on it that your father will help you with your French.
6. it用在if和when引导的结构里
在if/when引导的结构里，it没有实际上的意义。此类结构的表现形式一般是：when it comes to…，if it comes to that
When it comes to the Chinese culture including classical Chinese nobody knows more than
I don’t really trust him — nor his wife, if it comes to that.
If it is convenient to you, I want to ask you to help me repair the roof of the kitchen next weekend.
7. it用在that/this is和think sb. is句式里
That is it, This is it