Suppose that the index model for stocks A and B is estimated from excess returns with the following results: RA = 0.03 + 0.7 RM + eA RB = -0.02+ 1.2 RM + eB M =0.20; R-square A = 0.25 R-square B = 0.20 What is the standard deviation of A & B, respectively? Group of answer choices 0.28, 0.54 0.50, 0.45 0.54, 0.28 0.45, 0.50