Assume that interest rates on 20-year Treasury and corporate bonds are as follows:
T-bond = 7.72% AAA = 8.72% A = 9.64% BBB = 10.18%
The differences in these rates were probably caused primarily by:
a. Tax effects.
b. Default risk differences.
c. Maturity risk differences.
d. Inflation differences.
e. Real risk-free rate differences