She's always been kind to me—I can't just turn______on her now that she needs my help.
【正确答案】 A
【答案解析】解析：题干：她对我一直很好——既然她现在需要我的帮助，我不能不管。turn one's back on sb．是习惯用语，意思是“不理睬，拒绝帮助”，所以选A。