The correct answer is D. through dual fabric interconnects.
Cisco UCS X-Series achieves management high availability by using a pair of Fabric Interconnects (FIs), which provide redundant connectivity and management-plane resiliency for the chassis and its components. In UCS architecture, the fabric interconnects are the central control and management point for the compute domain, so deploying them as a redundant pair ensures that management access and infrastructure communication continue if one FI fails.
Option A is incorrect because UCS Director is an orchestration platform, not the native HA mechanism for UCS-X management components. Option B is incorrect because UCS Manager is associated with classic UCS domains and is not described as separate redundant manager instances in this context. Option C is also incorrect because Cisco Intersight is a SaaS or appliance-based management platform, but UCS-X high availability at the domain level is not achieved by running multiple Intersight instances.
The actual device-level resiliency for management in UCS-X comes from the redundant fabric interconnect design, which protects management and connectivity paths for the chassis, I/O, and compute resources.
Therefore, dual fabric interconnects are the correct answer.