QUESTION 6 Assume that interest rates on 20-year Treasury and corporate bonds with different ratings, all of which are noncallable, are as follows: T-bond = 7.72% A = 9.64% AAA = 8.72% BBB 10.18% The differences in rates among these issues were most probably caused primarily by: OA. Real risk-free rate differences OB. Tax effects OC. Default risk and liquidity differences D.Maturity risk differences OE. Inflation differences