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 campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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