题目

阅读理解Daylight Saving Time (DST) is the practice of setting the clocks forward one hour from standard time during the summer months (=lose 1 hour), and back again in the fall (=regain 1 hour), in order to make better use of natural daylight. So spring forward, fall back is one of the little sayings used to remember which way to set your watch.In 1966, Congress passed the Uniform Time Act, which standardized the length of DST, which begins on the second Sunday of March each year and ends on the first Sunday of November. In 2021, Daylight Saving starts at 2 a.m. on March 14 and it will end垫球是排球队常规训练的重要项目之一．下列图表中的数据是甲、乙、丙三人每人十次垫球测试的成绩．测试规则为连续接球10个，每垫球到位1个记1分．　　　　　　　　　　运动员甲测试成绩表测试序号12345678910成绩（分）7687758787 （1）写出运动员甲测试成绩的众数为_____；运动员乙测试成绩的中位数为_____；运动员丙测试成绩的平均数为_____；（2）经计算三人成绩的方差分别为S甲2=0.8、S乙2=0.4、S丙2=0.8，请综合分析，在他们三人中选择一位垫球成绩优秀且较为稳定的接球能手作为自由人，你认为选谁更合适？为什么？（3）甲、乙、丙三人相互之间进行垫球练习，每个人的球都等可能的传给其他两人，球最先从甲手中传出，第三轮结束时球回到甲手中的概率是多少？（用树状图或列表法解答）