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设一批零件 的长度服从正态分布N（μ，δ^2）,其中μ，δ^2均未知，现从中抽取16个零件，测得样本均值x=20cm与样本方差s=1cm,则μ的置信度为0.90的置信区间是（）
A.[20-1/4t0.05(16),20+1/4t0.05(16)]
B.[20-1/4t0.1(16),20+1/4t0.1(16)]
C.[20-1/4t0.05(15),20+1/4t0.05(15)]
D.[20-1/4t0.1(15),20+1/4t0.1(15)]
A.[20-1/4t0.05(16),20+1/4t0.05(16)]
B.[20-1/4t0.1(16),20+1/4t0.1(16)]
C.[20-1/4t0.05(15),20+1/4t0.05(15)]
D.[20-1/4t0.1(15),20+1/4t0.1(15)]
参考答案