i shall never forget the years -----i lived in the country w

i shall never forget the years _____i lived in the country with my grandfather ,_____has a great effect on my life.
A which,which B when,which C which,that D when,who
第一空我明白,麻烦讲下第二空 谢
就是说，第二个从句的先行词，为什么一定是the years 而不是 grandfather？