Sister sent me a picture of ________, which had been taken on the Great Wall.
A.MotherB.my mother'sC.mother'sD.mother在线课程A
解析：
巧解
分析：a picture of Mother my mother译为：妈妈的一张照片，指妈妈本人的照片。a picture of my mother's译为：妈妈的一张照片，但照片上不一定是妈妈本人。所以答案选A。