Which of the following statements is CORRECT? Portfolio diversification reduces the variability of returns (as measured by the standard deviation) of each individual a.stock held in a portfolio The required return on a firm's common stock is, in theory, determined solely by its market risk. If the market risk is b.known, and if that risk is expected to remain constant, then no other information is required to specify the firm's required return If an investor buys enough stocks, he or she can eliminate through diversification, 100% of the systematic risk inherent c. in owning stocks. A security's beta measures its non-diversifiable, or market, risk relative to that of the optimal market portfolio (where the Od tangent line hits the risky efficient frontier)