请问iv. 为什么不对呢？

问题如下：

The efficient frontier is defined by the set of portfolios that, for each volatility level, maximizes the expected return. According to the capital asset pricing model (CAPM), which of the following statements are correct with respect to the efficient frontier?

i. The capital market line is the straight fine connecting the risk-free asset with the zero beta minimum variance portfolio.

ii. The capital market line always has a positive slope and its steepness depends on the market risk premium and the volatility of the market portfolio.

iii. The complete efficient frontier without a risk-free asset can be obtained by combining the minimum variance portfolio and the market portfolio.

iv. The efficient frontier allows different individuals to have different portfolios of risky assets based upon their own risk aversion and forecast for asset returns.

v. The efficient frontier assumes no transaction costs, no taxes, a common investment horizon for all investors, and that the return distribution has no skewness.

选项：

ii, iii and v

i, ii and iii

i, iv and v

ii, iii and iv

解释：

Within modern portfolio theory (MPT), the efficient frontier is a combination of assets that has the best possible expected level of return for its level of risk. The efficient frontier is the positively sloped portion of the opportunity set that offers the highest expected return for a given risk level. The efficient frontier is at the top of the feasible set of portfolio combinations. ii, iii and v are correct statements.

在现代投资组合理论(MPT)中，有效边界是相对于其风险水平下具有最佳预期回报水平的资产组合。
有效边界是在给定风险水平下提供最高预期回报的机会集中的正倾斜部分。
有效边界位于可行组合集的顶端。Ii, iii和v是正确的表述。