Which of the following is an appropriate reason for maintenance testing?

Maintenance testing is a type of testing that is performed after a software product has been delivered and deployed to ensure that it still meets its requirements and functions correctly after changes have been made to it or to its environment. Changes can include corrective changes (fixing defects), adaptive changes (adapting to new platforms or environments), perfective changes (improving performance or usability), or preventive changes (avoiding potential problems). One of the appropriate reasons for maintenance testing is to verify that the software product works as expected after upgrading the operating system, which is an example of an adaptive change. Other reasons for maintenance testing can include verifying that the software product works as expected after fixing defects, adding new features, improving performance, or preventing future issues. You can find more information about maintenance testing in Software Testing Foundations: A Study Guide for the Certified Tester Exam, Chapter 12.