问题如下图：
选项：
A. 
B. 
C. 
解释：
方差已知用z分布，未知用t分布，A为什么是错的？
NO.PZ2015120604000132问题如下 Whiof the following is the most accurate statements about hypothesis testing?A.The calculatez-statistic for a test of a single varianis known as: z= X ¯ − μ 0 σ/ n (σ2 is the variance).B.If the computez-statistic = -3 anthe criticz-value = -2, the null hypothesis shoulaccepteC.the probability of the Type I error equals the significanlevel. C is correct. The z-statistic is usefor the test of the menot varian .If the computez-statistic = -3 anthe criticz-value = -2, the null hypothesis shoulrejecte type 1 error等于显著性水平，请问是怎么推导出来的？还有A，明白是检验均值的，想确认下关于Z statistic的计算公式是对的吗？
NO.PZ2015120604000132问题如下Whiof the following is the most accurate statements about hypothesis testing?A.The calculatez-statistic for a test of a single varianis known as: z= X ¯ − μ 0 σ/ n (σ2 is the variance).B.If the computez-statistic = -3 anthe criticz-value = -2, the null hypothesis shoulaccepteC.the probability of the Type I error equals the significanlevel. C is correct. The z-statistic is usefor the test of the menot varian .If the computez-statistic = -3 anthe criticz-value = -2, the null hypothesis shoulrejecte a怎么错了 麻烦下
NO.PZ2015120604000132 If the computez-statistic = -3 anthe criticz-value = -2, the null hypothesis shoulaccepte the probability of the Type I error equals the significanlevel. C is correct. The z-statistic is usefor the test of a sample menot varian. If the computez-statistic = -3 anthe criticz-value = -2, the null hypothesis shoulrejecte 请问type1 error课上有讲到吗？好像没有吧
NO.PZ2015120604000132 没有明白B为何不对，请帮忙解答。谢谢。
NO.PZ2015120604000132 A没有看懂，可以详细一下吗
