Comprehensive and Detailed Explanation:

The CMMC Assessment Process (CAP) allows for assessments of specific enclaves within an organization, defined as a segmented set of system resources sharing a common security perimeter. The CMMC Assessment Scope - Level 2 supports this by permitting the scope to be limited to an enclave if it fully contains the CUI environment and is properly isolated. While a CAGE code and SAM registration are required for the parent organization (the aerospace company), they are not mandated for individual enclaves within that entity. Since the company has these credentials, the assessor can proceed with a Level 2 assessment of the enclave, provided its isolation and security controls are verified.

Option B is incorrect as no rule prohibits enclave-only assessments. Option C is too broad, contradicting segmentation allowances. Option D misapplies level restrictions. A is correct per the CAP and scoping guide.