A CPA firm performs the annual audit of The Leahy Group, a private company. Leahy asks the firm to perform advisory services on a contingent fee basis. Which statement best describes when the firm would be prohibited from performing the services on a contingent fee basis under the AICPA Code of Professional Conduct?

a) During the period the firm is engaged to perform the audit and the period covered by the audited financial statements.

b) During the period covered by the audited financial statements.

c) During the period the firm is engaged to perform the audit up until the date on which Leahy pays its audit fee in full.

d) During the period the firm is engaged to perform the audit.