问题如下：
Which of the following tests of a hypothesis concerning the population mean is most appropriate?
选项：
A.A z-test if the population variance is unknown and the sample is small
B.A z-test if the population is normally distributed with a known variance
C.A t-test if the population is non-normally distributed with unknown variance and a small sample
解释：
B is correct.
The z-test is theoretically the correct test to use in those limited cases when testing the population mean of a normally distributed population with known variance
所以，总结来看，这里最关键的点在于是否是 small 样本的，不管知不知道variance都在其次？？？
是吗老师
