What does the tail boom of a rotary wing aircraft house?

The correct choice indicates that the tail boom of a rotary wing aircraft houses the tail rotor driveshaft. The tail boom is a critical structure that connects the main airframe of the helicopter to the tail section, where the tail rotor is located. The driveshaft specifically serves to transmit power from the engine to the tail rotor, allowing it to produce thrust that counteracts the torque effect generated by the main rotor. This counteracting force is essential for maintaining directional control during flight.

The other choices do not accurately reflect what is found in the tail boom. For instance, the main rotor is located on top of the helicopter's main fuselage, not within the tail boom. Cockpit controls are situated in the cockpit area for pilot access and operation, while gearboxes and fuel lines are typically located in different parts of the aircraft designed for structural integrity and maintenance accessibility. The tail boom's design and function are specifically oriented towards supporting the tail rotor and its associated components, making option B the most appropriate answer.