介词的位置
—般情况下，介词应放在它所支配的名词、代词或动名词之
前。但是，当介词出现在定语从句、动词不定式或以疑问词开头的
句中时，该介词通常要后置(尤其是日常用语中)。例如：
Who are you waiting for? 你在等谁?
who did you travel with? 你和谁一起旅行的?
This is the bookstore I got the dictionary from．
这就是我买字典的那家书店。
I gave him a piece of paper to write on.
我给他—张写字的纸。
然而，当有关的动词是“动词+介词，构成的短语时，则介词须
跟在动词后面。例如；
What are you looking at?
你在看什么?
The children she was looking after are very naughty.
她照看的那些孩子很顽皮。