1）介詞后面的關(guān)系詞不能省略。

　　2）that前不能有介詞。

　　3）某些在從句中充當(dāng)時(shí)間，地點(diǎn)或原因狀語(yǔ)的"介詞+關(guān)系詞"結(jié)構(gòu)可以同關(guān)系副詞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？