The lorry driver was badly _____ when his lorry crashed into a wall. A. damaged B. hit C. hurt D. harmed 答案:C 解析: damage损坏;harm对......有害;hurt(精神上或肉体上)伤害; hit打击;pain(精神上或肉体上)痛苦。甲、乙两台机床同时生产同一种零件,在10天中两台机床每天出的次品个数分别为:
甲:2,1,1,0,1,1,0,1,2,1,
乙:2,0,1,1,0,2,1,1,0,2.
统计员已计算出.
请你计算出乙机床的平均数和方差,并分析计算结果,判断哪台机床的性能较好?