Comprehensive and Detailed Explanation:

The CMMC Assessment Scope - Level 2 includes assets under the OSC’s control that process, store, or transmit CUI/FCI (Option B), secure these assets (Option C), or are managed by third parties (e.g., ESPs) handling CUI/FCI (Option D). Government assets transmitting CUI into the OSC’s systems (Option A) are out of scope, as they fall under a separate government authorization boundary and are not managed by the OSC. The scoping guide explicitly excludes such assets, making A the correct answer.