The answer is: A) They provide a source of energy
We currently generate our electricity by putting magnet on spinning turbine (the faster the turbine rotate, the more electricity that we can generate)
By creating dams, we can control the flow of water in the dam by closing or opening the dams' doors. This flow of water is strong enough to rotate the turbine to generate electricity. This is why we can say that dams provide source of energy.
