题目

When she was alone at home，Mary needed a friend __________. A.playing with                                          B.having played with C.with whom to play with                   D.with whom to play 答案：D 解析: with whom to play为“介词+关系代词+不定式”结构在句中作定语,其相当于一个定语从句(with whom she could play)。已知关于x的方程3x-2m+1=0与2-m=2x的解互为相反数，则m=         .