）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。
　 this is the house in which i lived two years ago.
　 this is the house where i lived two years ago.
　 do you remember the day on which you joined our club?
　 do you remember the day when you joined our club?