I still remember the day she first wore that pink dress.

C.
I still remember the day in which she first wore that pink dress.哦。我错了，是A。在定语从句的where=in which; when=on whichI still remember the day on which she first wore that pink dress. 其中on which she first wore that pink dress 为the day 的定语，即she first wore that pink dresson the day。