老师好，本题的A选项，视频讲解里说，前半段话是正确的，这个说反了吧？应该是前半段话是错误的吧？因为题目中说的是：error terms are uncorrelated with each other. 但是serial correlation 的定义是：error terms are correlated with one another.所以应该A里面serial correlation may be present 是错误的吧？谢谢老师。
A security’s systematic risk is proportional to：
A
the covariance of its return with the return on the market portfolio.
B
the standard deviation of its return.
C
the variance of its return.
D
its diversifiable risk.
这题的公式，课程里没有讲解，能讲解下吗
