碰到理解不了的定语从句时,可以把定语从句分解成简单句.
when 和where在引导定语从句时,在从句中做状语.
which,that,who引导定语从句时,在从句中做主语或宾语
以例句一来说
I'll never forgot the days.
we stayed in beijing on those days.一般情况下,when 是可以用介词+which代替的.stay即可以做及物动词也可以做不及物动词 .当及物动词时,就用on which做引导词；不及物时用when做时间状语
而在例句二中,从句还原后变成了 we spent those days in bejing.
spend 是及物动词,后边必须跟宾语,因此只能用which.比如：They spend an hour on their homework.