关系副词when主要用于修饰表时间的名词，同时它在定语从句中用作时间状语。下面为大家介绍定语从句中when的用法，希望对你有用！
定语从句中when的用法
when：当主句中的先行词(即主句中被后面定语从句修饰的词)是表示时间意义的名词时,它只能作定语从句的时间状语,放在定语从句句首.如果定语从句的引导词是作该定语从句的主语或宾语,则要改用关系代词that或which来引导.例如：
The days when we used foreign oil are gone.我们用洋油的日子一去不复返了.
I'll never forget the day when I was born.(=I'll never forget my birthday.) 我永远不会忘记我出生的'日子.
It happened in November when the weather was wet and cold.这事发生在天气又湿又冷的十一月.
In the years that (which) followed,Marx kept on studying English and using it.在这之后的几年中,马克思继续学习和使用英语.(that作定语从句"that followed"的主语)
The day (that) I always remember in all my life is my birthday.我一生中最难忘的日子是我的生日.(that作定语从句"that I always remember in all my life"的宾语,that可以省略)
追问：
He will never forget the days "when" he stayed with his students 这句怎么理解？为什么用when
追答：
the days 这个先行词在定语从句 he stayed with his students中没做主语，也没作宾语而是作状语，先行词做时间状语时用when
