What is the minimum amount of fuel required in MAIN Tanks 2 and 3 for the operation of APU/ATM systems?

The minimum amount of fuel required in MAIN Tanks 2 and 3 for the operation of the APU/ATM systems is indeed set at 4,500 lbs. This requirement is crucial for ensuring that the APU has adequate fuel to operate efficiently and effectively. If the fuel level drops below this threshold, it can lead to insufficient fuel supply for the APU, which could compromise its performance.

APUs require a reliable fuel source for efficient function, especially when powering systems that are essential during ground operations, such as starting engines and providing electrical power and environmental control. By specifying a minimum fuel requirement, safety and reliability in operations are prioritized, maintaining the operational readiness of the aircraft.

The other fuel quantity options are set higher than necessary for minimum operation, making B the most accurate and contextually appropriate answer.