,CPA's is a regional CPA firm that employs 100 professional and 20 support staff. In addition, the firm has 8 partners. Sam is the managing partner and has be a CPA for 25 years. His son Tommy is also a partner in the firm. The firm has various methods to charge fees to its clients. One of those methods, which of the following would be considered a contingent fee?

A) A protest of property tax assessment where a fee only be charged if the protest is successful.

B) Charging higher hourly rates for tax services than for bookkeeping services.

C) Charging higher hourly rates for manager's time than for a senior staff person's time

D) None of the above are considered contingent fees.