门口站着一位警察.用英语怎么说第二个问题；What was your wife doing while you were working in the garden?你在花园干活的时候,你妻子在做什么?请教的是为什么前面用was 后面用were?

Police stood a door.

(There is) a policeman standing at the door.

门口站着一位警察。
There is a policeman standing at the door.
while时两个动作同时进行, 都用进行时(时态一致)
your wife = she 第三人称单数 is的过去时= was
you are的过去时= you were

There is a policeman standing outside the door.
前面是单数，后面you 后自然要用are,只不过这里是过去时were.

There is a policeman standing the front of the door！

A policeman stood outside.
were 原因同上

with a policeman standing outside
was的主语是your wife,而were的主语使you

There is a policeman standing by the door.
By the door stands a policeman.
wife是第三人称用is 过去时就是was
you是第二人称,用are,过去时就是were