介词+关系词
1)介词后面的关系词不能省略。
2)that前不能有介词。
3)某些在从句中充当时间，地点或原因状语的介词+关系词结构可以同关系副词when 和where 互换。例如：
This is the house in which I lived two years ago. 这是我两年前住过的房子。
This is the house where I lived two years ago.
Do you remember the day on which you joined our club? 还记得你加入我们俱乐部的那一天吗?
Do you remember the day when you joined our club?
18.6 as, which 非限定性定语从句
由as, which 引导的.非限定性定语从句，as和which可代整个主句，相当于and this或and that。As一般放在句首，which在句中。例如：
As we know, smoking is harmful to ones health. 如我们所知，吸烟有害健康。
The sun heats the earth, which is very important to us. 太阳使地球暖起来，这对我们人类很重要。
典型例题
1)Alice received an invitation from her boss, ___came as a surprise.
A. it B. that C. which D. he
答案C. 此为非限定性从句，不能用 that修饰，而用which.，it 和he 都使后句成为句子，两个独立的句子不能单以逗号连接。况且选he句意不通。
判断关系代词与关系副词
方法一： 用关系代词，还是关系副词完全取决于从句中的谓语动词。及物动词后面无宾语，就必须要求用关系代词；而不及物动词则要求用关系副词。例如：
This is the mountain village where I stayed last year.
Ill never forget the days when I worked together with you.
判断改错（注：先显示题，再显示答案，横线；用不同的颜色表示出。）
（错） This is the mountain village where I visited last year.
（错） I will never forget the days when I spent in the countryside.
（对） This is the mountain village （which） I visited last year.
（对） Ill never forget the days （which） I spent in the countryside.
习惯上总把表地点或时间的名词与关系副词 where, when联系在一起。此两题错在关系词的误用上。
方法二： 准确判断先行词在定语从句中的成分（主、谓、宾、定、状），也能正确选择出关系代词/关系副词。
例1. Is this museum ___ you visited a few days age?
A. where B. that C. on which D. the one
例2. Is this the museum ____ the exhibition was held.
A. where B. that C. on which D. the one
学识谷
