问题如下：
The riskless rate of interest is r = 5% and the market portfolio is characterized by E(RM) = 13% and σM = 15%.
CAPM implies that the expected return of stocks A, B, and C are
选项：
A. E(RA) = -3%, E(RB) = 5%, E(Rc) = 21%
B. E(RA) = -5%, E(RB) = 3%, E(Rc)= 21%
C. E(RA) = 3%, E(RB) = 5%, E(Rc) = 16%
D. None of the above
解释：
A is correct..
E(RA) = -3%, E(RB) = 5%, E(Rc) = 21%
In equilibrium stocks are on the same security
market line:
E(Ri) = r + [E(RM) - r]βi
这题的解题思路是什么？贝塔未知，怎么求回报率？