Which of the following statements is most correct?

a. Risk refers to the chance that some unfavorable event will occur, and a probability distribution is completely described by a listing of the likelihood of unfavorable events. b. Portfolio diversification reduces the variability of returns on an individual stock. c. When company-specific risk has been diversified the inherent risk that remains is market risk, which is constant for all securities in the market. O d. A beta of 1.00 means that excess returns for the stock vary proportionally with excess returns for the market portfolio