Yahoo Finance reported the following market betas for the stocks of selected health insurers: Beta Company United Health Group Humana Aetna Cigna 0.70 1.16 0.63 0.71 Assume that the risk-free rate, RF, and required rate of return on the market, R(Rm), are 2.0 percent and 8.5 percent, respectively. a. What are the required rates of return on the four stocks? b. Which of the stocks is riskiest for investors? Explain your