The following table summarizes the yields to maturity on several one$-$year, zero$-$coupon securities: $.($Note: The yields displayed in the table are annually compounded yields.$)$

a$.$What is the price $($expressed as a percentage of the face value$)$ of a one$-$year, zero$-$coupon corporate bond with an 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?