介词分为简单介词，如：at, in, on, besides, since, for等；合成介词，如：inside, outside, without, within, into, onto等；短语介词（或成语介词），
如：because of, in front of, instead of, in spite of等；
二重介词，如：from behind, until after等。
The key to the door is missing.
The water-tower in front of our school was built in 1988.
Some students are in the classroom, and some on the playground.
As we know,
Did you see a pen under my desk this morning?
They have sent another rocket into the sky.
1) On Sundays, the family are mostly out. （时间状语）
2) On top of the hill stands a TV tower. （地点状语）
3) He is used to sleeping with all the windows open. （伴随状语）
4) In the search for the lost child, the villagers went all out. （目的状语）
5) All the work must be done by hand. （方式状语）
6) At times, I go to the cinema. （频度状语）
7) She is by far the best student in our class. （程度状语）
8) Because of poverty, he couldn’t go to school. (原因状语)
9) To my surprise, he got the first prize in the contest. （结果状语 / 或评注性状语）
10) Without our Party, we couldn’t live a happy life. （条件状语）
11) In spite of great efforts we failed to carry our plans through. （让步状语）
12) As a matter of fact, nobody agreed to his project. （评注性状语）
In my opinion, you’d better go with us.
“介词＋宾语＋补足语”可以构成介词的复合结构，在句子当中可充当表语、定语、状语、补语等。这种结构中的宾语和补足语之间存在着逻辑上的主谓关系，使得句子意义更加丰富。常见的这类介词有with, without, like, of等。
He is used to sleeping with all the windows open.
Bamboo leaves swing in the wind like slim fingers reaching to touch something.
At the beginning of school, the noise of desks being opened and closed and lessons (of being) repeated at the top of the children’s voices could be heard out in the street.
The wounded boy glared at the nobleman with his teeth clenched.
The cat humped its back just like a fierce tiger to jump upon me.
The little boy rushed out of the house without anything on.
The teacher entered the classroom with a book under his arm.
The naughty boy suddenly rushed out from behind the tree to frighten the girl.
In the spring, new bamboo shoots come out from around their own roots.
He kept on working until after lunch.
Not knowing what to do, the worried officer walked up and down the room.
There are many trees in and outside the town.
Please come in. (in为副词 = into the room)
We have no car, but we can go there without. (without为副词 = without a car)
Although the exam was difficult, I managed to get through. (through为副词 = through the exam)