NO.PZ2018062016000099
问题如下：
In a standard normal distribution, which of the following parameter does not equal zero？
选项：
A. Skewness
B. Variance
C. Mean
解释：
B is correct. In a stabdard normal distribution, the mean and the skewness all equal zero.
正态分布里不是mean=median=mode么 为啥等于0