问题如下：
By which degree can a portfolio affect the risk and return proflie?
选项：
A.Portfolios equally affect risk reduction and return enhancement.
B.Portfolios affect more on risk reduction.
C.Portfolios affect more on return enhancement.
解释：
B is correct.
Portfolios affect more on risk reduction.
老师 这个知识点出现在讲义哪里？
