1.I didn't know you were in London.How long have you been he

1.I didn't know you were in London.How long have you been here?
首句为什么用一般过去时呢?根据第二句,“you"现在还在伦敦啊,我觉得应该用完成时啊.
2.Tom slipped into the house when no one was looking him.
我不太明白主句和从句的时态.从句我觉得应该用一般过去时.
3.Do you have any clothes to be washed today?
Your hair is too long.You should have your hair cut.
我不太明白第一句中为什么用不定式的被动.如果表示将来,第二句中也有将来的意思,为什么不用不定式的被动呢?
4.The temple was found to be empty.
为什么要用to be
5.It is such a warm today.
这原本是一道选择题,选项中有It is so warm today这个选项,为什么不选他呢?
6.He helped me whenever I asked him to.
为什么不能用whatever呢?
7.The students expected there being more classes.
为什么是being呢?
8.He found his house to have been broken into.
宾补为什么是不定式的完成时呢?
9.An old friend from abroad,whom I was expecting to stay with me,telephoned from the airpot.
这里的whom为什么不能用who代替?不是只有在介词后面who才不能代替whom吗?
10.My friends was very unhappy for not to have been invited to the concert.
for后面不是该加v-ing形式吗?
11.I must get up earlier tomorrow morning not to be late again.
I must get up earlier tomorrow morning so as not to be late again.
第二句中的so as not to be late again应该是作状语吧?那第一句中的not to be late again又是个什么呢?
12.This year's production is four times what it was 10 years ago.
解释中说what=that which,那that做什么成分,which呢?
13.I don't mind you/your delaying making the decision.
you/your是delaying的逻辑主语吧?make 为什么用v-ing形式?
14.The twin sisters are so alike that no one can tell who is who.
Who is it?It's me.
第一个句中的第二个who是表语却用了主格,第二句中的me是表语却用了宾格,为什么呢?
15.His corn grew very well this year,so at harvest time they gave us quite a lot of it.
为什么不能用much of it?
16.New baby food will be sent to whoever phones us first.
为什么不用whomever?
17.If you build a house without permission,you will be ordered to demolish what you have built.
(既然是将来时,为什么不用will have built?）
18.There was an accident on the street and since then there has been a severe congestion of traffic.
since then 为什么不能被after that代替?
19.It's hard to find a researcher who is also a good teacher.
定语从句为什么不能是who teaches also very well?
20.George doesn't know where they put the lawn mower after they had finished using it.
为什么不能用where to put the lawn mower?
21.What type of automobile would you buy if you were free to choose among all the cars available today?
为什么不能用if all the cars available were free to be chosen by you?

2.Tom slipped into the house when no one was looking him.
我不太明白主句和从句的时态.从句我觉得应该用一般过去时.
when引导的从句是进行时,对主句的动作有一种不满的情绪,这句
话应该译成：当没有人注意的时候,他却偷偷地溜进来了.
例如：
Someone knocked at the door when I was having breakfast.
此句应译成,我正在吃早饭的时候,他妈的竟然有人敲门.
就是对主句的不满.