at,in,on ~~~!急

用at,in,on
1.please put the things___the desk.
2.l can't find anything_____the box.
3.look!ther is a big dog_____the door.
4.he put up the poster____the notice board.
5.don't sit_____the floor!it is dirty.
6.don't lie ____bed!
7.now sit_____this chair.
8.the vegetables were grown____the garden.
9.now the books are all___the shelves.
10.i found some boxes___the cellar.
11.i came across a friend ___my way to work.
12.there is a little church___the top of the small hill.
13.you must knock____the door before you come in.
14.a small accident happend____board the ferry.
15.look!there is a cow ____the field.