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.
不是当样本数量增加，N自由度也是增加，置信区间不是更宽吗？
