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别看it拼写简单，读音规则，可是，在现行初中英语教材中，与它相关的句型还真不少呢！
一、it用作形式主语的句型
英语中常常见到某个句子以it开头，it与其后面的动词不定式短语、动名词短语、名词性从句等相呼应，以表达一个完整的意义。这是一种习惯表达法，这样的句式可避免句子显得头重脚轻。it用作形式主语的句型主要有以下几种：
1. “It is / was adj. (for / of sb.) to do sth.” 这一句型中，究竟用for还是用of，一般遵循这样的规则：如果形容词仅仅是描述事物的，如difficult, easy, hard, important, dangerous等，用for；如果形容词是描述不定式行为者的性格、品质的，如kind, good, nice, clever等，则用of。例如：
It is interesting to play with snow in winter. 冬季时玩雪是很有趣的。
It’s important for us to keep the water clean. 保持水质清洁对我们来说是很重要的。
It’s very kind of you to help me. 你帮助我真是太好了。
温馨提示：这一句式中的形容词位置也可换用名词；连系动词be也可换用其它连系动词，如feel等。例如：
It’s a good habit to get up early and go to bed early. 早睡早起是好习惯。
It must be great fun to fly to the moon in a spaceship. 乘宇宙飞船飞往月球一定很有趣。
It feels strange to have a twin sister. 有个孪生姐妹，感觉很奇怪。
2. “It is / was / will be adj. / n. V-ing短语” ，其中it是形式主语，V-ing短语是真正的主语。例如：
It’s bad playing in the street. 在街上玩是没好处的。
Is it any good trying again? 再试一次有用吗？
It was no use believing him. 相信他是没用的。
3. “It is / was adj. / n. that从句”，其中that从句是真正的主语。例如：
It is certain that he will come. 他一定会来。
It’s clear that you are right. 很清楚你是对的。
It is a pity that you haven’t passed the examination. 你没有通过考试是个遗憾。
4. “It is / was one’s turn (duty, pleasure) to do sth.” 意为“该轮到某人做某事(做某事是某人的责任、愉悦的事)”。例如：
It’s your turn to be on duty tomorrow. 明天轮到你值日了。
It’s your turn to read now. 现在轮到你读了。
5. “It takes / took (sb.) some time to do sth.” 意为“干某事花了(某人)多少时间”。例如：
It’ll take only five minutes to walk there. 步行到那里只需要五分钟时间。
It took me a week to finish reading the book. 我花了一周时间看完这本书。
6. “It cost / costs sb. some money to do sth.” 意为“某人花多少钱做某事”。例如：
It cost me 260 yuan to buy the new watch. 我买这块新手表花了260元。
It cost me 5,000 yuan to buy the new computer. 我买这台新电脑花了5000元。
7. “It 系动词(look, seem, appear等) 从句”，意为“似乎/看起来……”。如：
It looks that he has been there before. 看起来他好像以前到过那儿。
It seems that he is happier now than yesterday. 看起来他好像比昨天高兴些了。
8. “It is / was said（reported, learned…） that从句” 意为“据说(据报道，据悉……)”。例如：
It is said that he has come to Beijing. 据说他已经到北京了。
It is reported that the bridge was washed away. 据报道这座桥被冲走了。
二、it用作形式宾语的句型
当句子的真正宾语是动词不定式、动名词或从句时，为避免句子头重脚轻，须将其放在宾语补足语之后，改用先行词it占据其原来的位置。it用作形式宾语的句型主要有以下几种：
1. “Sb. thinks / finds / believes /… it adj. (for sb.) to do sth.” 意为“某人认为(发现、相信……)干某事是……”。例如：
He found it not easy to learn a foreign language well. 他发现学好一门外语是不容易的。
I feel it necessary to hold a meeting to discuss the problem. 我感到有必要召开一次会议来讨论这个问题。
2. “Sb. thinks / finds / believes / … it adj. that从句” 意为“某人认为(发现、相信……)……”。例如：
I think it important that we should master English. 我认为我们掌握英语是很重要的。
I find it unnecessary that you should reply to this letter. 我发现你没有必要回这封信。
3. “Sb. thinks / finds / believes / … it n. to do sth.” 意为“某人认为(发现、相信……)……”。例如：
I feel it my duty to help her. 我觉得自己有责任帮助她。
We make it a ruler to listen to BBC for 15 minutes every day. 我们把每天听15分钟BBC电台广播作为一个规定来执行。
三、与it相关的其它句型
1. “It is / was time for sth.” 或 “It is / was time (for sb.) to do sth.” 意为“是该(某人)干某事的时候了”。例如：
It is time for lunch. 该吃午饭了。
It is time to go home. 该回家的时候了。
It is time for you to play games. 现在你们该做游戏了。
2. “It is / was / has been 时间段 since 一般过去时” 意为“自从……以来已过了……(时间)”。该句型主要用来处理非延续性动词的完成时，又要和表示一段时间的时间状语连用的问题。主句中时间作表语，其时态是现在时或完成时，since引导的从句通常是一般过去时态，而且是非延续性动词。如果主句是一般过去时，从句则用过去完成时。例如：
It’s ten years since I came here. 我来这儿已经有10年了。
It’s been four days since I caught a cold. 我感冒已四天了。
It was only three days since he had left here. 他离开这儿仅三天。
温馨提示：如果这一句型中since从句的谓语动词是延续性的，则意为“自从不……有多长时间了”，即应将从句谓语译为否定。试比较：
It is five years since he married. 自从他结婚有五年了。(marry是非延续性动词)
It is five years since he was married. 他离婚有五年了。(be married是延续性动词)
一、it用作形式主语的句型
英语中常常见到某个句子以it开头，it与其后面的动词不定式短语、动名词短语、名词性从句等相呼应，以表达一个完整的意义。这是一种习惯表达法，这样的句式可避免句子显得头重脚轻。it用作形式主语的句型主要有以下几种：
1. “It is / was adj. (for / of sb.) to do sth.” 这一句型中，究竟用for还是用of，一般遵循这样的规则：如果形容词仅仅是描述事物的，如difficult, easy, hard, important, dangerous等，用for；如果形容词是描述不定式行为者的性格、品质的，如kind, good, nice, clever等，则用of。例如：
It is interesting to play with snow in winter. 冬季时玩雪是很有趣的。
It’s important for us to keep the water clean. 保持水质清洁对我们来说是很重要的。
It’s very kind of you to help me. 你帮助我真是太好了。
温馨提示：这一句式中的形容词位置也可换用名词；连系动词be也可换用其它连系动词，如feel等。例如：
It’s a good habit to get up early and go to bed early. 早睡早起是好习惯。
It must be great fun to fly to the moon in a spaceship. 乘宇宙飞船飞往月球一定很有趣。
It feels strange to have a twin sister. 有个孪生姐妹，感觉很奇怪。
2. “It is / was / will be adj. / n. V-ing短语” ，其中it是形式主语，V-ing短语是真正的主语。例如：
It’s bad playing in the street. 在街上玩是没好处的。
Is it any good trying again? 再试一次有用吗？
It was no use believing him. 相信他是没用的。
3. “It is / was adj. / n. that从句”，其中that从句是真正的主语。例如：
It is certain that he will come. 他一定会来。
It’s clear that you are right. 很清楚你是对的。
It is a pity that you haven’t passed the examination. 你没有通过考试是个遗憾。
4. “It is / was one’s turn (duty, pleasure) to do sth.” 意为“该轮到某人做某事(做某事是某人的责任、愉悦的事)”。例如：
It’s your turn to be on duty tomorrow. 明天轮到你值日了。
It’s your turn to read now. 现在轮到你读了。
5. “It takes / took (sb.) some time to do sth.” 意为“干某事花了(某人)多少时间”。例如：
It’ll take only five minutes to walk there. 步行到那里只需要五分钟时间。
It took me a week to finish reading the book. 我花了一周时间看完这本书。
6. “It cost / costs sb. some money to do sth.” 意为“某人花多少钱做某事”。例如：
It cost me 260 yuan to buy the new watch. 我买这块新手表花了260元。
It cost me 5,000 yuan to buy the new computer. 我买这台新电脑花了5000元。
7. “It 系动词(look, seem, appear等) 从句”，意为“似乎/看起来……”。如：
It looks that he has been there before. 看起来他好像以前到过那儿。
It seems that he is happier now than yesterday. 看起来他好像比昨天高兴些了。
8. “It is / was said（reported, learned…） that从句” 意为“据说(据报道，据悉……)”。例如：
It is said that he has come to Beijing. 据说他已经到北京了。
It is reported that the bridge was washed away. 据报道这座桥被冲走了。
二、it用作形式宾语的句型
当句子的真正宾语是动词不定式、动名词或从句时，为避免句子头重脚轻，须将其放在宾语补足语之后，改用先行词it占据其原来的位置。it用作形式宾语的句型主要有以下几种：
1. “Sb. thinks / finds / believes /… it adj. (for sb.) to do sth.” 意为“某人认为(发现、相信……)干某事是……”。例如：
He found it not easy to learn a foreign language well. 他发现学好一门外语是不容易的。
I feel it necessary to hold a meeting to discuss the problem. 我感到有必要召开一次会议来讨论这个问题。
2. “Sb. thinks / finds / believes / … it adj. that从句” 意为“某人认为(发现、相信……)……”。例如：
I think it important that we should master English. 我认为我们掌握英语是很重要的。
I find it unnecessary that you should reply to this letter. 我发现你没有必要回这封信。
3. “Sb. thinks / finds / believes / … it n. to do sth.” 意为“某人认为(发现、相信……)……”。例如：
I feel it my duty to help her. 我觉得自己有责任帮助她。
We make it a ruler to listen to BBC for 15 minutes every day. 我们把每天听15分钟BBC电台广播作为一个规定来执行。
三、与it相关的其它句型
1. “It is / was time for sth.” 或 “It is / was time (for sb.) to do sth.” 意为“是该(某人)干某事的时候了”。例如：
It is time for lunch. 该吃午饭了。
It is time to go home. 该回家的时候了。
It is time for you to play games. 现在你们该做游戏了。
2. “It is / was / has been 时间段 since 一般过去时” 意为“自从……以来已过了……(时间)”。该句型主要用来处理非延续性动词的完成时，又要和表示一段时间的时间状语连用的问题。主句中时间作表语，其时态是现在时或完成时，since引导的从句通常是一般过去时态，而且是非延续性动词。如果主句是一般过去时，从句则用过去完成时。例如：
It’s ten years since I came here. 我来这儿已经有10年了。
It’s been four days since I caught a cold. 我感冒已四天了。
It was only three days since he had left here. 他离开这儿仅三天。
温馨提示：如果这一句型中since从句的谓语动词是延续性的，则意为“自从不……有多长时间了”，即应将从句谓语译为否定。试比较：
It is five years since he married. 自从他结婚有五年了。(marry是非延续性动词)
It is five years since he was married. 他离婚有五年了。(be married是延续性动词)