I'll never forget the days (which) I spent in the countryside. 中为什么要用which而不用when?是不是因为spent是及物动词?

I promise I'll never forget . i think I'll never forget you I'll never forget in my whole I'll Never Forget You 歌词 mariah ,I will never forget you .I'll miss you 英语作文 the person i`ll never forget 80词 I’ll never forget ___ you for the first time. I'll never forget our promise forever什么意思? 求I'll never forget my friend 英语作文 求I'll never forget…… 英语作文 I'll never forget the day( )we met I’ll never forget the days _____________ we worked together I’ll ____ forget your help.A.always B.never I'll never forget you这里加个will 是做什么的啊?直接写个i never forget you I'll never forget the factory ___ (what/which) I worked five years agoI'll never forget the factory ___ (that/which) I worked five years ago i never forget We were happy that time and i'll never forget it.We _____ ______ be happy that time and i'll never forget it . I'll never forget the days ___ I joined the League(填介词)