介詞+關係詞
1)介詞後面的關係詞不能省略。
2)that前不能有介詞。
3)某些在從句中充當時間，地點或原因狀語的介詞+關係詞結構可以同關係副詞when 和where 互換。例如：
This is the house in which I lived two years ago. 這是我兩年前住過的房子。
This is the house where I lived two years ago.
Do you remember the day on which you joined our club? 還記得你加入我們俱樂部的那一天嗎?
Do you remember the day when you joined our club?
18.6 as, which 非限定性定語從句
由as, which 引導的.非限定性定語從句，as和which可代整個主句，相當於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. 如我們所知，吸煙有害健康。
The sun heats the earth, which is very important to us. 太陽使地球暖起來，這對我們人類很重要。
典型例題
1)Alice received an invitation from her boss, ___came as a surprise.
A. it B. that C. which D. he
答案C. 此為非限定性從句，不能用 that修飾，而用which.，it 和he 都使後句成為句子，兩個獨立的句子不能單以逗號連接。況且選he句意不通。
判斷關係代詞與關係副詞
方法一： 用關係代詞，還是關係副詞完全取決於從句中的謂語動詞。及物動詞後面無賓語，就必須要求用關係代詞；而不及物動詞則要求用關係副詞。例如：
This is the mountain village where I stayed last year.
Ill never forget the days when I worked together with you.
判斷改錯（注：先顯示題，再顯示答案，橫線；用不同的顏色表示出。）
（錯） This is the mountain village where I visited last year.
（錯） I will never forget the days when I spent in the countryside.
（對） This is the mountain village （which） I visited last year.
（對） Ill never forget the days （which） I spent in the countryside.
習慣上總把表地點或時間的名詞與關係副詞 where, when聯繫在一起。此兩題錯在關係詞的誤用上。
方法二： 準確判斷先行詞在定語從句中的成分（主、謂、賓、定、狀），也能正確選擇出關系代詞/關係副詞。
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
學識谷
