What are the characteristics of a security that actually matter for a rational investor? a. Risk and the cost of capital b. Risk only c. Risk and return d. Return only Why does a risk-free security have zero variance (or zero standard deviation)? a. Because the expected return is always greater than the actual return b. Because the actual returns are always zero c. Because the actual return is always equal to the expected return d. Because the expected return is always lower than the actual return