Consider the basic mean$-$variance model with long$-$only constraints and no riskless asset. Which of the individual asset classes must lie on the efficient frontier?

Select one

A$.$ The asset class with the lowest volatility

B$.$ The asset class with the highest expected return

C$.$ The asset class with the lowest volatility and the asset class with the highest expected return

D$.$ Neither the asset class with the lowest volatility nor the asset class with the highest expected return