题目解析:
以一个磨轮为例,说明了封闭系统的能量供应是有限的。线索:The energy supply of a closed system is limited and is progressively used up by the processes operating within the system; Without any additional energy supplied from the outside, the system fs processes stop altogether...; Once the container of water is empty, the wheel no longer turns because there is no water to turn it.