It is half past two now.（指时间）
It is six miles from here to the nearest hospital.（指距离）
It is a lovely day, isn't it?（指天气）
—What's this? —It's a panda.
I had a talk with Mary and it was helpful.
There is a knock on the door, go to see who it is.
Wow! What a lovely baby! Is it a he or she?
It is dangerous for you to swim in the river.
We feel it our duty to make our country a better place.
6.用于强调句中。It is / was +被强调部分+that / who
It was at the palace ball that Mathilde lost her necklace last night.
It is a pity / shame that真可惜
It is no wonder that难怪
It seems / appears that似乎
It happens that碰巧
It occurs to/ comes to / strikes / hits sb. that某人突然想起
It is said / reported that所说
It is no use / good doing做某事没有好处
It is (high) time that......should do / did是该做某事的时候了
It it the first time that sb. have / has done sth.是某人第一次做某事
It is / has been......since 自从……已经……时间了
It will be / was ......before还要……时间才
It takes sb. some time to do sth. 做某事花费某人多长时间
see to it that 确保
count /> as someone puts it 正如某人所说
when it comes to 提及；谈到
appreciate it if如果……将不胜
I take it that我的理解是
it, one , ones, that, those
I can't find my hat. I din't know where I put it. （it就指代前文的hat)
Your pen is so beautiful. I also want to buy one.（one就指代前文提到的pen这类事物中的一个即可）
4.that经常用于比较级中，指代一个单数或不可数名词，指代单数时可以与the one替换; 指代复数名词时用those。如
The population of Shanghai is larger than that of Qingdao.（that指代population，不可数名词)
The hat you bought is bigger than that I bought.（that指代hat，可数名词单数，可以与the one替换）
The TV sets we made this year are better than those we made last year.（those指代TV sets，复数）