I will never forget the days ________ I spent in the countryside.

问题描述:

I will never forget the days ________ I spent in the countryside.
应该是which,为什么不是when

which I spent in the countryside是定语从句,修饰the days,which在定语从句中作spend的宾语.when是副词,无法充当spend的宾语.
若果要用when,就将句子改成I will never forget the days when I lived in the countryside.