问题如下：
If X1 and X2 are independent, and both have univariate normal distributions, is the joint distribution of X1 and X2 a bivariate normal?
选项：
解释：
It would be if these are independent, because this is a bivariate normal with 0 correlation.
这道题会有具体的例子吗？ 或者怎么推出来的呢？
