Straight Bonds are the most common type of bond. Which of the characteristics below does not apply:

a$.$ Legal obligation to pay the bondholder a fix sum at the bond's maturity.

b$.$ Payment of periodic payment $($coupon$)$ during the life of the bond.

c$.$ The face value of the bond will not change during the life of the bond.

d$.$ The price of the bond will always be at its par $($face$)$ value.