1.介詞短語既可以作狀語,又可以作表語、定語和賓補.作狀語時,可以前置也可以后置；作定語必須后置；作表語要放在系動詞之后；作賓補要放在賓語之后：
In the office there are two desks= There are two desks in the office.
He is in the room.The man in the room is my uncle.I find her in the room.
2.狀語有三個位置：句首、句中、句尾
On top of the mountain he saw a grand temple.
He stayed in the cave.He slowly stepped into the cave.