Look at the four squares,A ,B ,C , and D, which indicate where the following sentence could be added to the passage. Where would the sentence best fit？
For example, the hot tea in a vacuum bottle does not interact with the environment outside the bottle.
A closed system is isolated from its surroundings.A The energy supply of a closed system is limited and is progressively used up by the processes operating within the system.B The ability of the system to function decreases as the available energy is exhausted. Without any additional energy supplied from the outside, the system's processes cease altogether and no further change is possible in the system.C A mill wheel supplied with water from a non- refillable container is a closed system. Once the container of water is empty, the wheel no longer turns because there is no water to turn it. In a truly closed system, the water would have to be collected below the mill wheel in a second container to ensure that the system did not supply any energy to the outside.D

A. Square Ａ.
B. Square Ｂ.
C. Square Ｃ.
D. Square Ｄ.