Which of the following is a basic component of the air conditioning pack?

The correct answer highlights the heat exchanger pack as a basic component of the air conditioning pack due to its critical role in the climate control system of an aircraft. The heat exchanger pack functions by transferring heat away from the air to be cooled before it is circulated within the cabin, thereby maintaining a comfortable environment for crew and passengers. This component is essential for regulating the temperature of the air conditioning system, ensuring efficiency in cooling and heating as needed.

In the context of the air conditioning system, the fuselage structure is primarily the framework of the aircraft. While it supports various systems, it is not a direct component of the air conditioning pack itself. The environmental control unit is a broader term that encompasses multiple elements involved in managing the aircraft's atmosphere but does not specifically refer to the component that directly cools or heats the air. The slow flight system pertains to aerodynamic characteristics and control at lower speeds, which is unrelated to the operation of the air conditioning system.