What is the key difference between required return and realized return?

a$.$ Realized return considers the risk of the investment and required return does not.

b$.$ Realized return and required return have similar meanings and are interchangeable terms.

c$.$ Realized return is what actually happens; required return is the return sought given the risk of the investment.

d$.$ Realized return is the return sought given the risk of the investment; required return is what actually happens.