I'll never forget the day I was born．
A. when
B. that
C. on which
D. both A and C
网友回答
A. when
B. that
C. on which
(答案→)D. both A and C
解析：考查定语从句。本定语从句的先行词是the day,定语从句的结构很完整，主语是I，后面是系表结构，句子很完整，故使用关系副词，先行词指时间，故使用关系副词when, 关系副词经常等于介词+关系代词。本题when=on which.故D正确。