18) Based on current dividend yields and expected capital gains, the expected rates of return on Portfolio A and B are 11% and 14%, respectively. The beta of A is 0.8 while that of B is 1.5. The T-bill rate is currently 6%, while the expected rate of return of the S&P 500 Index is 12%. The standard deviation of portfolio A is 10% annually, while that of B is 31%, and that of the index is 20%. If you could invest only in T-bills and one of the three portfolios (A, B, S&P 500 Index), which would you choose? Please explain. (5 points)