已知一批零件的长度 sim N(mu ,1) ,随机抽取1-|||-6个零件得到长度的平均值为40,则这一批零件-|||-的长度的置信系数为0.95的置信区间为(附-|||-.025=1.96)()-|||-(A)(38.4,42.5);-|||-(B)(39.51,40.49);-|||-(C)(37.23,39.51);-|||-(D)(38.52,42,31).