问题如下：
Tim, an analyst of an investment company, says "If we increase the sample size only, both the standard error and the confidence interval width will reduce. " Tim's statement is:
选项：
A.correct.
B.incorrect about confidence interval.
C.incorrect about the standard error.
解释：
A is correct.
By increasing the sample size, the estimation of population parameter is more accurate. Therefore, the standard error will decrease, and confidence interval will become narrower.
除了sample size大小以外，confidence interval是不是也取决于confidence level的大小？这里好像没有提及到这点，何老师上课好像还强调了这点。
