问题如下：
With respect to capital market theory, an investor’s optimal portfolio is the combination of a risk-free asset and a risky asset with the highest:
选项：
A.expected return.
B.indifference curve.
C.capital allocation line slope.
解释：
B is correct.
Investors will have different optimal portfolios depending on their indifference curves. The optimal portfolio for each investor is the one with highest utility; that is, where the CAL is tangent to the individual investor’s highest possible indifference curve.
optimal portfolio是无差异曲线和CAL的切点可以理解，但是无差异曲线有很多条，为什么说和CAL相切的那个就是highest的？怎么判断哪一个无差异曲线是highest indifference curve呢？
