Answer:
Open system.
Explanation:
Thermodynamics mainly deals with the exchange of energy and matter in the systems and surroundings. Three main type of systems are open system, closed system and isolated system.
An open system is the system in which energy and matter can be move easily from the system to the surroundings and vice-versa. This system is known as constant volume system.
Thus, the system in which energy and matter can move freely is the open system.
