The efficient frontier of risky assets is

the portion of the investment opportunity set that lies above the global minimum variance portfolio.

both the portion of the investment opportunity set that lies above the global minimum variance portfolio and the portion of the investment opportunity set that represents the highest standard deviations.

the portion of the investment opportunity set which includes the portfolios with the lowest standard deviation.

the set of portfolios that have zero standard deviation.

the portion of the investment opportunity set that represents the highest standard deviations