This type of appraisal may be conducted every 24 months after a Benchmark appraisal as long as the Organizational Unit (OU) remains eligible.

The correct answer is "Sustainment" because it pertains specifically to the ongoing evaluation of an organization's processes following a Benchmark appraisal. In the context of the Capability Maturity Model Integration (CMMI), a Sustainment appraisal is designed to ensure that the organization maintains its maturity level over time and continues to follow best practices established during the initial assessment.

The Sustainment appraisal typically occurs every 24 months as long as the Organizational Unit (OU) remains eligible, demonstrating a commitment to continuous improvement and compliance with CMMI standards. This type of appraisal helps organizations to monitor their progress and address any gaps that may arise after the initial Benchmark appraisal.

Understanding Sustainment appraisals is crucial for organizations looking to maintain their maturity levels and ensure that they do not regress in their practices. Other appraisal types, while related, do not fit this specific timeline or purpose as precisely as Sustainment does.