Which statement is TRUE?

a)We would generally find that the beta of a single is more stable over time than the beta of a diversified portfolio

b)If an investor buys enough stocks, he or she can, through diversification, eliminate all of the market risk inherent owning stocks, but as a general rule it will not be possible to eliminate all diversifiable risk

c)A firm can change its beta through managerial decisions, including capital budgeting and capital decisions

d)Under the CAPM, the required rate of return on a firm's common stock is determined only by the firm's standard deviation.