问题如下：
When discerning the difference between population means, then most accurate test is :
选项：
A.z-test.
B.paired comparisons test.
C.chi-square test.
解释：
B is correct. The t-test in this section is based on data arranged in paired observations, and the test itself is sometimes called a paired comparisons test.
paired comparions test 不是是samples not independent吗 可题目里面不是说的是population，不对应，为什么是选这个呢，谢谢
