NO.PZ2020010304000003
问题如下：
If X1 and X2 are independent, what is the correlation between X1 and X2?
选项：
解释：
Independent random variables always have a correlation of 0. This statement is only technically true if the variance of both is well defined so that the correlation is also well defined.
This statement is only technically true if the variance of both is well defined so that the correlation is also well defined
这句话是什么意思呢
