问题如下：
An increase in sample size is most likely to result in a:
选项：
A.wider confidence interval.
B.decrease in the standard error of the sample mean.
C.lower likelihood of sampling from more than one population.
解释：
B is correct.
All else being equal, as the sample size increases, the standard error of the sample mean decreases and the width of the confidence interval also decreases.
不太能理解，为什么n 越大，置信区间越窄？ n越大不是，更精准吗？ n越大犯一类错误的阿发就更小吧，置信区间不是应该更大吗？ 概念有点混
