Final answer:
The nurse is conducting a retrospective evaluation by mailing a client satisfaction questionnaire to a client who was discharged from the hospital four days ago.
Step-by-step explanation:
The nurse is conducting a retrospective evaluation by mailing a client satisfaction questionnaire to a client who was discharged from the hospital four days ago. In a retrospective evaluation, data is collected after an event or process has occurred, such as after the client's discharge from the hospital. This type of evaluation allows the nurse to assess the client's satisfaction and gather feedback to identify areas for improvement.