一道高考题, 分析一下句子结构和意思.

题目

一道高考题, 分析一下句子结构和意思.
A good friend of mine from___ i was born showed up at my home right before i left for beijing

A how B whom C when D which

答案

C
我的一个小时候的好朋友在我即将去北京的时候出现在我家门口.
a good friend of mine 主语
show up 谓语
at my home 地点状语
before i lfet for beijing 时间状语
from when i was born 定语