问题如下：
If a population sampled is normally distributed with a known variance, which of the following statements on a hypothesis tests of the population mean is most accurate?
选项：
A.z-test.
B.t-test.
C.F-test.
解释：
A is correct, if the population sampled is normally distributed with a known variance, then the test statistic for a hypothesis test concerning a single population mean, the Z-test is applied.
这里sampled的意思不是样本方差已知吗？总体方差未知，不是应该用t检验吗？
