Which individuals are subject to PSIs for security determinations?

The correct answer is that military, civilian, and contractor personnel affiliated with the DoD are subject to Personnel Security Investigations (PSIs) for security determinations. This encompasses a broad range of individuals who may have access to sensitive information or positions that require a certain level of trustworthiness and reliability. The Department of Defense (DoD) mandates PSIs to ensure that everyone involved, whether they are service members, government employees, or contractors, are properly vetted, thus maintaining national security.

Understanding the importance of PSIs is critical: they help assess an individual's background, character, and conduct to determine their eligibility for positions of trust. This is crucial when considering the sensitive nature of work within the DoD and the potential impact on national security from any breach of confidentiality or trust. Therefore, the inclusion of all three groups emphasizes a comprehensive approach to personnel security.

The other options incorrectly limit the scope of individuals who require PSIs. By focusing solely on military personnel, civilians, or contractors, these options overlook the collaborative nature of defense operations, where all types of personnel can access sensitive information or critical roles. Thus, the correct answer underscores the extensive and inclusive nature of personnel security within the DoD framework.