在相同观测条件下,用钢尺对某段距离丈量了六次,其结果为:146.535米, 146.548米, 146.541米, 146.550米, 146.537米, 146.546米。试求其距离的算术平均值x,一次丈量距离的中误差m,算术平均值的中误差M及其相对中误差K (2.0分) A. 146.543m ±9mm ±4mm 1/38722 B. 146.543m ±6mm ±4mm 1/38722 C. 146.543m ±6mm ±2mm 1/38722 D. 146.543m ±6mm ±2mm 1/58722