设基础清漆的干燥时间 approx N(mu ,(sigma )^2), σ未知,现抽取9个样品,测得样本均值-|||-x=6(小时), 样本标准差 s=1(小 时),则μ的置信水平为0.95的置信区间为 ()-|||-(A) (6pm dfrac (1)(9)(t)_(0.025)(8))-|||-B ) (6pm dfrac (1)(3)(t)_(0.025)(8))-|||-(C) (6pm dfrac (1)(9)(t)_(0.025)(9))-|||-( D) (6pm dfrac (1)(3)(t)_(0.025)(9))