The Security Market Line ("SML" or CAPM) is:

A.) the same as the Capital Allocation Line ("CAL").

B.) a theoretic value, but of little consequence to investors in the real world.

C.) a relationship of Standard Deviation to expected returns.

D.) a relationship of Standard Deviation to required returns.

E.) a function implying disequilibrium if the returns of a security do not plot on the line.

Please explain why you choose your answer, thank you!