The following table summarizes the yields to maturity on several one-year, zero-coupon securities Security Treasury AAA corporate BBB corporate B corporate Yield (%) 3.12 3.21 4.24 4.88 with a AAA rating? b. What is the credit spread on AAA-rated corporate bonds? c. What is the credit spread on B-rated corporate bonds? d. How does the credit spread change with the bond rating? Why