it adj to do sth语法分析
“it adj to do sth”结构中，it是形式主语，真正的主语是后面接的动词不定式短语。adj是形容词，用来描述后面的动词不定式短语。整个结构的意思是“做某事是某种状态（形容词）”的意思。例如：
It's important to study hard.（努力学习很重要。）
It's difficult to learn a new language.（学一门新语言很难。）
It's easy to make mistakes.（犯错误很容易。）
在这些例句中，it是形式主语，真正的主语是后面的不定式短语；adj用来描述后面的不定式短语的状态。这种结构常用来表示一些客观的或大众共识的事实、情况或观点。
what day is it today语法点
What day is it today？
今天星期几？
What day is…，是询问星期的句型。在这亇句型中，whay day 是询问星期的固定搭配词组，在句中作表语。
it是主语，但并无具体指代。通常用it来表示天气，气候和星期几。在口语中，该句型中的it常被省略。is是联系动词。在疑问句中主谓语序倒装了。today是时间状语。
这句回答的句型是It is (星期几)。
如，It is Monday today.
今天星期一。
或:It's Monday.今天星期一。
What day is it today语法点是it代替today作了形式主语，对真正主语today起强调作。it作形式主语不仅可以代替像today这样的名词，还可以代替从句等。例如 lt was yesterday when he came(他来的时间是昨天).这里it代替主语从句when he came作形式主语，对when起到了强调作用。
it was he语法
强调主语的时候，前面it was 后面用的就是主语形式的代词
例：It was he that bought the book in this shop yesterday.
it is（was,were）...that...是强调句,强调的是is和that之间的内容.这里强调的是he，他在这家商店买的书📖。
举一返三:
1．被强调成分是主语，who/that之后的谓语动词应该在人称和数上与原句中的主语保持一致:
. It is I who am right．
It is he who is wrong．
It is the students who are lovely．
2．即使被强调成分是句子中的时间状语，地点状语，原因状语等，也不能用when，where, because，要用that。
如:
It was after the war was over that Einstein was able to come back to his research work again .
It was in front of the bank that the old lady was robbed．
It was because of the heavy rain that he came late．
3．如果被强调的成分有同位语，同位语也应提前。
It was from him，his chemistry teacher，that Paul learned to watch carefully in class．
4．被强调成分是作主语的代词，用主格，是作宾语的代词，用宾格。
It was he that helped me yesterday. It was me that he helped yesterday.
5．被强调部分既包括人又包括物，用that不用who。
lt was the things and people that they remembered that they were talking about．
