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.
再问： 可答案说选A~~ 但还是谢谢你啦~
再答： 哦。 我错了，是A。 在定语从句的where=in which; when=on which I 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 dress on the day。