关系副词都等于一个适当的介词＋which,在从句中作状语
When=in/at/on/…+which;
Where=in/at/on/…+which;
Why=for /…+which
1.Do you still remember the day when(on which) we went to visit the museum together?
2.This is the factory where(in which)my father once worked.
3.This is the reason why(for which) he was late.