Which of the following gives the best definition of the CAPM approach?

a) Unsystematic risk, as measured by beta, is the only factor affecting the level of return required on a share for a completely diversified investor.

b) Unsystematic risk, as measured by beta, is one of the key factors affecting the level of return required on a share for a completely diversified investor.

c) Systematic risk, as measured by beta, is the only factor affecting the level of return required on a share for a completely diversified investor.

d) Systematic risk, as measured by beta, is one of the key factors affecting the level of return required on a share for a completely diversified investor.