Which one of the following statements about Investment Opportunity Set $($IOS$)$ in the two dimensional $($expected return E$($r$)$ and standard deviation $\backslash$sigma $)$ scatter diagram is CORRECT?

Question $3$ options:

When mixing a risky and a risk$-$free assets together, the IOS is a curve.

When mixing two risky assets together, the IOS is a straight line.

When mixing a risky and a risk$-$free assets together, all the portfolios on IOS have the same sharp ratio.

When mixing two risky assets together, all the portfolios on IOS have the same sharp ratio.