18.5 介詞+關(guān)系詞
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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)時間，地點或原因狀語的"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?