on the day that you were born 是什么结构?

题目

on the day that you were born 是什么结构?
on the day that you were born, your mother died. 这句里面,
“that you were born “ 是什么结构, 是一个定语从句么?
我理解的是 ： that you were born 是定语从句
也就是， 主句是， on the day, your mother died.
但是如果这样的话， 那么先行词 day 在主句中做什么成分呢？ 时间状语？ 定语从句的先行词可以是时间状语么？
那么用when 也可以么？ on the day when you were born, your mother died.

答案