Answer:
D. an insulated thermos
Step-by-step explanation:
A closed system is a type of system that does not allow transfers in or out of the system. Therefore, the best example of this would be an insulated thermos. The fact that the thermos is insulated means that the system is designed to allow as little as possible transfer in or out of the system. In the case of the thermos, the transfer would be one of heat.