Water wheels are machines that use the energy of（）to turn a wheel.The axle of the turning wheel can then power other machines to do work.

Water wheels are machines that use the energy of（）to turn a wheel.The axle of the turning wheel can then power other machines to do work.
A.flowing water
B.neither of them
C.or falling water
D.or both
正确答案：flowing water；or falling water；or both