矩‖，动差任意变量的正整数功效的期望值‖。第一个矩是分配的平均数 The expected value of a positive integral power of a random variable. The first moment is the mean of the distribution.
人们使用轧机把材料加工成各种形状‖，如圆棒材、方棒材和矩形棒材‖。 A rolling mill is used to form the material into various form such as round rod, square or rectangular bar.
