The following table summarizes the yields to maturity on several $1-$year, zero$-$coupon securities:

a$.$ What is the price $($expressed as a percentage of the face value$)$ of a $1-$year, zero$-$coupon corporate bond with

a AAA$-$rating and a face value of $$1,000?$

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?

Note: Assume annual compounding.