Which of the following statements concerning beta are correct? I. Adding stocks with high betas to a portfolio increases the portfolio's market risk. II. The higher the beta, the higher the expected return. III. A beta can be positive, negative, or equal to zero. IV. A beta of 0.5 indicates a lower level of risk than a beta of 1.5.

A. I and IV only

B. II and III only

C. I, II, III and IV

D. II, III and IV only