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 by:
a. real risk-free rate differences
b. tax effects
c. default risk differences
d. maturity risk differences
e. inflation differences