问题
单项选择题
A certain ball was dropped from a window 8 meters above a sidewalk. On each bounce it rose straight up exactly one-half the distance of the previous fall. After the third bounce the ball was caught when it reached a height of exactly 1 meter above the sidewalk. How many meters did the ball travel in all ？（）
A．21
B．19
C．17
D．15
E．13
答案
参考答案：A
解析：
该球从窗户上落下共8米，而第一次反弹的高度为4米，来回共8米，第二次反弹的高度为2米，来回共4米，第三次反弹的高度为1米，球在达到第三次反弹的最高点时被抓住，所以该球共走了：
8+4×2+2×2+1=21米。