- However, after a year or so in which they became more serious about their work, the Monkees started to play and sing their own songs like a real band.
in which此处引导定语从句修饰a year or so,可换成when,“介词+关系代词which”大多可转换成关系副词来引导定语从句。
I shall never forget the day on which (=when) we moved into our new house.
答案：①Is this the place at which (=where) the traffic accident occurred?
②We don’t know the reason for which (=why) she didn’t come to the party.