题目

（2010·天津蓟县下营中学高三第一次模拟）   1. National holiday is _____ time for leisure. But making good use of _____ time is not easy for most Chinese. A. a; a            B. a; the         C. the; /          D. the; a 答案：B1．数列1$\frac{1}{2}$，3$\frac{1}{4}$，5$\frac{1}{8}$，7$\frac{1}{16}$，…，（2n-1）+$\frac{1}{{2}^{n}}$，…的前n项和Sn的值等于n2+1-$\frac{1}{{2}^{n}}$．