we will never forget the days ---we spent with your family 这

when.定语从句,用when 修饰the days
不明白的再问哟,请及时采纳,多谢!
再问： 为什么不能用on which呢？
再答： 用on which 的话,还原一下句子：we spent on the days with your family.你觉得通吗？