请问不能使用其他三个distribution进行检验的原因是什么？

问题如下：

An analyst wants to test whether the standard deviation of return from pharmaceutical stocks is lower than 0.2. For this purpose, he obtains the following data from a sample of 30 pharmaceutical stocks. Mean return from pharmaceutical stocks = 8%. Standard deviation of return from pharmaceutical stocks = 12%. Mean return from the market = 12%. Standard deviation of return from the market = 16%. What is the appropriate test statistic for this test?

选项：

A.

t-statistic

B.

z-statistic

C.

F-statistic

D.

χ2 statistic

解释：

Tests of the variance (or standard deviation) of a population requires the chi-squared test.