关系代词:
主 格 who which that
宾 格 whom that that
所有格 whose of which/whose of which/whose
关系副词=介词+关系代词
例如：where=in which,when=on which,why=for which
例句：
1 the year when he was born (when = in which)
=the year in which he was born
2 the day when they arrived (when = on which)
3 the hotel where they were staying (where = in/at which)
4 the reason why he refused is .