Which of the following statements about the minimum$-$variance frontier is CORRECT?

a$.$ The minimum$-$variance frontier only includes high$-$risk portfolios.

b$.$ It includes portfolios that offer the best risk$-$return combinations from the global minimum$-$

variance portfolio and upward.

c$.$ All portfolios on the minimum$-$variance frontier ate equally efficient.

d$.$ It represents portfolios with the highest risk and return.