题目

 Danny is playing        and Tom is playing       . A. piano, football               B. a piano, a football C. piano, the football            D. the piano, football 答案：D18．设随机变量的分布列如表所示，且E（ξ）=1.6，则ab=（　　）ξ0123P0.1ab0.1A．0.2B．0.1C．0.15D．0.4