Assume that interest rates on 20-year Treasury and corporate bonds with different ratings 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:

a.

Tax effects.

b.

Real risk-free rate differences.

c.

Inflation differences.

d.

Maturity risk differences.

e.

Default risk and liquidity differences.