Final answer:
The activity that would not impair the independence of a CPA firm is posting client-approved entries to a client's trial balance.
Step-by-step explanation:
The activity that would not impair the independence of a CPA firm regarding an audit client is b. Post the client-approved entries to a client's trial balance.
The independence of a CPA firm is important to ensure that the audit process is unbiased and objective. Performing activities such as authorizing credit applications, using information-processing facilities to prepare payroll, signing tax returns, and advising client management can all potentially impair independence.