1：it 做形式主语，不定式to do 或that 引导的句子做真正的主语
　　
　　例句: It is important for us to protect environment. 保护环境对我们来说是很重要的。（it 做形式主语，真正的主语是to protect environment）即 to protect environment is important for us 是本句，但这样显得头重脚轻，所以用it 做形式主语.
　　
　　例句: It is common knowledge that science and technology is the first productive force.( it 做形式主语，that 引导的句子做真正的主语
　　
　　2：it 做形式宾语，不定式to do 或that 做真正的宾语
　　
　　例句：He thinks it very hard to master a foreign language.他认为掌握一门外语是很难的。（he做主语，thinks 做谓语，it 做形式宾语，very hard 做宾补，to master a foreign language 做真正的宾语，即He thinks to master a foreign language very hard.
　　
　　例句：He thinks it very essential that he should have a decent job.他认为他应该有一份体面的工作是很必要的即He thinks that he should have a decent job very essential.
　　
　　3: it 用于强调句，其结构是it is \was+强调部分+that
　　
　　例句：It was his carelessness that caused his fatal failure.正是他的粗心导致了他的致命失败。（强调his carelessness,做caused的主语,即强调主语）
　　
　　例句：It was in the cinema that I came across my former English teacher.在电影院我巧遇我的前任英语老师。(强调地点状语in the cinema)
　　
　　强调句去除it is 和that 这三个词依然还是完整的句子
　　
　　4 It引导时间的三种句型
　　
　　1：It is +一段时间+since 从句（从句用一般过去时）
　　
　　例句：It is a decade since we became friends.自从我们成为朋友已经有十年了。
　　
　　2: it was +一段时间+before 从句（从句用一般过去时）
　　
　　例句：It was several weeks before he found that his precise painting was missing.过了好几周他才发现他的宝贵画不见了。
　　
　　3 ：it will be +一段时间+before 从句（从句用一般现在时）
　　
　　例句：It will be a long time before China becomes a developed country.在中国成为发达国家之前将需过很长一段时间。
　　
　　语法单选
　　
　　1 It is his ability that _________________.
　　
　　A he has become a general manager B makes him become a general manager
　　
　　C why he can become a general manager D for which he becomes a general manger
　　
　　2 ________is very import for her ____________.
　　
　　A It , has complete her work in time B It , because she has to complete her work in time
　　
　　C It , to complete her work in time D There , to complete her work in time
　　
　　3 I think _____________________.
　　
　　A it is very crucial to save money B it very crucial saving money
　　
　　C it very crucial save money D it very crucial to save money
　　
　　4 It was his courage ______________.
　　
　　A that made him stand out B that he stood out
　　
　　C why he stood out D helped him stand out
　　
　　5 It _______ten years __________he became a teacher.
　　
　　A was , since B is, after
　　
　　C is, before D is , since
　　
　　6 It __________many hours __________his mother arrives home.
　　
　　A will be ,before B is , before
　　
　　C was , since D will be , before
　　
　　7 It ___________two years _________he found that he had caught the liver cancer.
　　
　　A was, before B was,since
　　
　　C has been ,when D is,before
　　
　　8 It was ____________that_____________.
　　
　　A because he spared no efforts to study ,made him become a top student.
　　
　　B because of his diligence that made him become a top student.
　　
　　C his diligence ,he became a top student
　　
　　D his diligence, made him become a top student.
　　
　　语法填空
　　
　　1 It is essential for students ________(keep)healthy.
　　
　　2 I feel ________very necessary for me to help her.
　　
　　3 It is only in this way _________we can achieve the instant fame.
　　
　　4 I feel __________very important _______we keep practicing English everyday.
　　
　　5 It __________two days __________the meeting ends.
　　
　　6 It _________two weeks _________we knew each other
　　
　　7 It __________a long time ________we become successful actors.
　　
　　8 It ___________ five days ________ we arrived in Macao.
　　
　　答案及解析（单选）
　　
　　1 B 【 解析】 强调句，因为it is his ability that 强调的是名词his ability ,只能做makes 的主语
　　
　　2 C 【解析】 it 放句首做形式主语，只能to do 或that 引导的句子做真正的主语
　　
　　3 D 【解析】it 放think 后做形式宾语，后面to do 做真正的宾语
　　
　　4 A 【 解析】 强调句，强调主语
　　
　　5 D 【解析】it is +一段时间+since 从句
　　
　　6 D 【解析】it will +一段时间+before 从句（从句用一般现在时态）
　　
　　7 A 【解析】it was +一段时间+before 从句（从句用一般过去时态）
　　
　　8 D 【解析】强调句 his diligence 做made 的主语
　　
　　答案及解析（语法填空）
　　
　　1 to keep 【解析】it 放句首做形式主语，to do 做真正的主语
　　
　　2 it 【解析】it 放feel 后做形式宾语，to help her 做真正的宾语
　　
　　3 that 【解析】强调句，强调部分only in this way 做方式状语
　　
　　4 it ,that 【解析】it 做feel 的形式宾语,后面是句子不是不定式
　　
　　5 will be ,before【解析】ends 是一般现在时，只适合it will be+一段时间+before 从句
　　
　　6 is ,since【解析】knew 是一般过去时态，根据意思，只适合it is +一段时间+since 从句
　　
　　7 will be ,before【解析】become 是一般现在时态，
　　
　　8 is ,since 【解析】arrived 是一般过去时态

！欢迎微信搜索“奇速优课”了解更多中高考冲刺抢分16讲相关信息，现在登录还可免费领取英语学习智能笔记本！电话咨询奇速英语袁老师18011421646何老师17711523911