问题如下图：
选项：
A. 
B. 
C. 
解释：
Is it okay to use all money to buy portfolio 6, not considering the diversification issue.
because all portfolio has risk lower than 15% and portfolio 6 has the highest excess return which is 14.29%. So, why cannot we just pick portfolio 6 so we can maximum return while still meet the risk requirement?
