英语特长的朋友,麻烦看下这2组定语从句：I will never forget the day on which I worked on the farm.
I will never forget the day when I worked on the farm.
That was a happy yearin which I workde with you.
That was a happy year when I worked with you.
我想知道什么时候将when 换成in which 或on which,怎么判断.