Each curve $($Tall $=$ Green, Medium $=$ Blue, Flat $=$ Red$)$ represents a stock portfolio with a mean return of $10\%.$ Which curve is the most desirable from a risk management perspective? Why is this? If we combine the portfolios represented by the Tall and Flat curves, what should we expect to happen to $($a$)$ average return, and $($b$)$ total risk as measured by variance? What assumptions are you making?