题目

已知全集，，则等于（ ）A.R B. C. D. 答案：【答案】C【解析】利用补集定义直接求解．解：全集，集合，集合．故选：． ____ most children nowadays are the only chidren, they tend to be more self-centered. A. Ever since           B. Now that         C. Only if          D. Even though