When should vehicles yield to taxiing aircraft?

Answer: C — At all times when taxiing aircraft are present

Vehicles should yield to taxiing aircraft at all times when they are present because safety is the paramount concern on an airfield. Taxiing aircraft have the right-of-way, and yielding to them ensures that potential collisions are avoided. The flight operations on an airfield are priority, and vehicles must adhere to this protocol to maintain a safe operating environment. This requirement applies regardless of visibility conditions or the size of the aircraft relative to the vehicle, thus emphasizing the importance of always being vigilant and yielding to any aircraft taxiing on the runway or taxiway. Maintaining this behavior reinforces proper airfield traffic management and upholds safety protocols for all personnel involved.