-- Look! The man is __________ the poster at the bus stop.
-- Let's go and stop him. We should keep our city clean.
A:putting out
B:putting up
C:putting away
D:putting down
甲、乙、丙三位选手各10次射击成绩的平均数均为9.3环,方差(单位:环2)依次分别为0.026、0.015、0.032.则射击成绩最稳定的选手是____ (填“甲”、“乙”、“丙”中的一个).
观察下列等式: 11×2=1−12 , 12×3=12−13 , 13×4=13−14 ,
将以上三个等式两边分别相加得: 11×2+12×3+13×4 =1﹣ 12+12−13−14 =1﹣ 14 = 34 .