1. 介词 + 关系副词 在意义上表示，从...的角度看；自从...时候起。以下第一组句子在意思上不具备这样的意思。

2. 介词 + 关系副词 在形式上 先行词必须是 介词 + 时间/地点 的一个状语 都是一个介词短语。研究一下第二组句子的先行词形式。 when/where 通常代指的是介词短语。 

注意： since后只能用where, 而不能用which  因为根据以上原则，副词应代指的是一个状语，而不是一个名词。

I'll never forget the time when we worked on the farm.

Do you remember the afternoon when we first met three years ago?

The hotel where we stayed wasn't very clean.

I'd like to live in a house where there is plenty

We went up to the roof of the temple, from where we had a good view of the procession.

They stood near the north window, from where they could see the whole garden.

Look over there! Some people are standing under the tree on the hill, from there you can enjoy the whole view.

That was in 1949, since when things have been better.

They left in Monday, since when  we have heard nothing.

I went to bed at ten, before when I was reading for an hour.

Next summer, by when the house should be ready.

 

 

1. He was blown off course and found himself in an unkown land, from where he eventually reached Greenland.

2. He stood under the tree, from where he could see his son swimming.
3. You can go across the river, from where you can take a boat.
4. The book was written in 1946, ___ the education system has witnessed great changes.

  A. when   B. during which   C. since then   D. since when

5.