For Which of the Following Would Polymorphism Not Provide a Clean

For which of the following would polymorphism not provide a clean solution?

A) A billing program where there is a variety of clients who are billed with different fee structures.
B) A maintenance log program where a variety of machine data is collected and maintenance schedules are produced for each machine based on the data collected.
C) A program to compute a 5% savings account interest for bank clients.
D) An IRS program that maintains information on a variety of taxpayers and determines who to audit based on criteria for classes of taxpayers.