1. There are two situations. If Zhou Ling doesn't know that Sanyuan Company is a client of the firm, it doesn't violate professional ethics; If you know that Sanyuan Company is a client of your own firm, you should strictly abide by the suspicion of avoiding interests and not buy shares of Sanyuan Company. If you know that you have business dealings after purchase, you should report it to the firm and clear the stock as soon as possible.

2. Bookkeeping by yourself and auditing by yourself violate professional ethics. According to the moral principle, you can only engage in one of the businesses and get rid of the other.

3. Accepting a computer violates professional ethics. If you strictly abide by it, you should refuse it.

4. Violation of professional ethics. Zhou Ling should be appointed by the firm to audit the annual statements of Pengfei Company.