一、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...He will never forget the days"when" he stayed with his students这句怎么理解？为什么用whenthe 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