24. According to the ethical standards of the profession, which of the following acts is generally prohibited?

A. Promoting management advisory services in a professional publication

B. Writing a financial management newsletter promoted and sold by a publishing company

C. Accepting a commission for recommending a product to an audit client

D. Accepting engagements obtained through the efforts of third parties

P.S: I know the answer is C, but can you explain more detail for each question and how come the correct is C??