Choice "D" is correct. Under Rule 302, contingent fees are permitted when they involve a legal proceeding or ruling. When a CPA is receiving a contingent fee for a private letter ruling, it would be allowed under Rule 302 and not be considered actually "contingent" because it would most likely be fixed by the legal jurisdiction. Choice "a" is incorrect. Contingent fees are prohibited for audits of a client's financial statements. Choice "c" is incorrect. Contingent fees are not allowed for a review engagement of a client's financial statements. Choice "b" is incorrect. Contingent fees are prohibited for an examination of a prospective client's financial information.