According to the ethical standards of the profession, which of the following acts generally is prohibited?
a. Accepting a contingent fee for representing a client in connection with obtaining a private letter ruling from the Internal Revenue Service.
b. Retaining client records after the client has demanded their return.
c. Revealing client tax returns to a prospective purchaser of the CPA's practice.
d. Issuing a modified report explaining the CPA's failure to follow a governmental regulatory agency's standards when conducting an attest service for a client.