问一个英语问题哈!I'll never forget the day ( ) we stayed in the country and the days ( ) we spent happily."( )"中填when 或which顺便问一下为什么

问一个英语问题哈!I'll never forget the day ( ) we stayed in the country and the days ( ) we spent happily."( )"中填when 或which顺便问一下为什么
问一个英语问题哈!
I'll never forget the day ( ) we stayed in the country and the days ( ) we spent happily.
"( )"中填when 或which
顺便问一下为什么

问一个英语问题哈!I'll never forget the day ( ) we stayed in the country and the days ( ) we spent happily."( )"中填when 或which顺便问一下为什么
第一个填when ,the day在后面的定语从句中做状语,由when引导；
第二个填which,the days在后面的定语从句中做宾语.

I'll never forget the day ( when ) we stayed in the country and the days ( which) we spent happily.

第一个括号里填when 第二个填which，因为第一个从句中却得是时间状语，就是at the day，而when等于at which，就可替换他做引导词 而后面从句缺的是宾语即the days ，就可直接用which来替代。

分别是when，which
we stay in the county ，主胃宾齐全，缺的是时间状语。which we spent happily，which充当spent（及物动词）的宾语