Available choices:
[A]. damming a river
[B]. power stations
[C]. freezing h2o
[D]. electricity
[E]. burning fossil fuels
[F]. hydrogen and oxygen
[G]. sunlight
[H]. nuclear meltdowns
Given those answer options, answer the question: Fact 1: Hydropower requires damming a river. Fact 2: Hydropower is a renewable, economical source of electricity. Given the two facts above, what does a renewable, economical source of electricity require?
A:
[A].