it的用法

用作代词

• The book is mine. It is interesting.
• Don't get close to that dog. It looks dangerous.

形式主语和形式宾语

• That NVIDIA stock will rise is confirmed. -> It's confirmed that NVIDIA stock will rise.
• Play computer games for too long is no good. -> It is no good playing computer games for too long.
• I find to get to the town in half hour almost impossible. -> I find it almost impossible to get to the town in half hour.

dummy it

• It is dark outside.
• It seems that he has been there for years.
• Just do it.

强调句

强调句结构：It + be动词 + 强调部分 + that…

Tom opened the box with a knife.

• It was Tom that opened the box with a knife.
• Was it the box that Tom opened with a knife?
• It was with a knife that Tom opened the box.