Assume that interest rates on 15-year noncallable Treasury and corporate bonds with different ratings are as follows:T-bond = 7.72%AAA = 8.72%A = 9.64%BBB = 10.18%The differences in rates among these issues were most probably caused primarily by:(ATax effects.B) Real risk-free rate differences.(C Default risk differences.(D Inflation differences.(EMaturity risk differences.