Final answer:
The BEST option to ensure that the software and instruments are working as designed is User acceptance testing.
Step-by-step explanation:
The BEST option to ensure that the software and instruments are working as designed is User acceptance testing. User acceptance testing is a process in which end-users test the system and provide feedback to ensure that it meets their requirements and functions properly. This testing verifies the system's ability to perform as expected in real-world scenarios.
System design documentation provides information about how the system should work, but it does not guarantee that it will work as intended. Peer review and static code analysis testing help identify potential issues in the code, but they do not directly test the system's functionality. Change control documentation is related to managing software changes and updates, but it does not ensure that the software and instruments are working correctly.