Answer:
c. a sinking fund call pays off a portion of the bond principal, while a refunding call issues new bonds to replace old ones.
Step-by-step explanation:
a sinking fund call involves using a portion of the funds set aside in a sinking fund to redeem a part of the bond's principal amount before it matures.
a refunding call, on the other hand, typically involves issuing new bonds at a lower interest rate to retire the existing bonds, thereby replacing the old debt with new debt at more favorable terms.