On the Challenger 300/350, which areas are equipped with a fire extinguishing system?

The correct choice highlights the areas equipped with a fire extinguishing system on the Challenger 300/350, specifically the Auxiliary Power Unit (APU), left engine, and right engine. Each of these components can pose a significant fire risk, necessitating robust fire suppression strategies.

For the left and right engines, the fire extinguishing system is critical because if a fire occurs in an engine compartment, rapid response is necessary to ensure the safety of the aircraft and its passengers. The APU, being a vital component that provides electrical power and bleed air when the main engines are not running, also requires fire protection due to its exposed fuel and operational mechanics. Each of these systems is strategically placed to enhance the aircraft's resilience to fire hazards.

The other options mention areas that are not typically equipped with a fire extinguishing system. For instance, while the cargo hold does have smoke detection systems, it does not have the direct fire extinguishing capabilities like the mentions in the correct answer. The same applies to the landing gear, which is not a primary area for fire hazards requiring extinguishing systems.