In the event of a loss of engine No. 2 or 3, which pump assists in landing gear retraction?

The correct response is the transfer pump. In the C-17 aircraft, the transfer pump plays a crucial role in the hydraulic system, particularly in ensuring that essential operations, such as landing gear retraction, can occur if there's a failure of engine No. 2 or 3.

When these engines are lost, the hydraulic system relies on the transfer pump to maintain pressure in the landing gear system, allowing the pilot to safely retract the landing gear. This is vital for maintaining aircraft performance and safety, especially during critical phases of flight right after an engine loss.

While the other pumps have their specific roles, such as providing primary hydraulic fluid under normal conditions or supporting other systems, the transfer pump is specifically designed to take over in scenarios where there's a loss of engine power, ensuring that the aircraft can still perform necessary functions like gear retraction safely.