My Corporation wishes to estimate its cost of retained earnings. The firm's beta is 1.3. The rate on 6-month T-bills is 2%, and the return on the S&P 500 index is 15%. What is the appropriate cost for retained earnings in determining the firm's cost of capital?
A. 17.0%
B. 19.5%
C. 18.9%
D. 22.1%