I：引导定语从句的关系副词有where, when和why.它们引导定语从句修饰表示地点、时间和原因的先行词，在从句中充当地点状语，时间状语和原因状语。
如：--She is going to live in Macao, where she has some close friends.
--Next month, when you'll spend your summer holidays in your hometown, is approaching.
--He didn't tell me the reason why he was so upset.
其中当先行词是表示地点，时间和原因的词时，是用关系代词还是关系副词一定要看该词在从句中的成分，
