For extended power failures, the best safeguard is a generator. CompTIA Security+ SY0-701 emphasizes that generators are designed to provide long-term, sustained power, unlike UPS systems, which only supply temporary emergency power.

Generators ensure that critical operations—including data centers, communication systems, and security infrastructure—stay online for hours or days, depending on fuel capacity. This matches the requirement for mitigating “extended” outages.

UPS units (C) protect against short-term outages and provide time for graceful shutdown or generator startup, but cannot support prolonged power consumption. Batteries (B) provide the least protection and run out quickly. Off-site backups (A) do not maintain operational continuity; they simply preserve data.

Disaster recovery and business continuity planning in SY0-701 highlights generators as essential components for maintaining availability, a core principle of the CIA triad. Generators prevent downtime, maintain productivity, and keep essential systems functioning throughout prolonged outages, making D the best answer.