Fact 1: Hydropower requires damming a river.

Fact 2: Hydropower is a renewable, economical source of electricity.

Given the two facts above, answer the question "what does a renewable, economical source of electricity require?" with the following options: 
- damming a river
 - power stations
 - freezing h2o
 - electricity
 - burning fossil fuels
 - hydrogen and oxygen
 - sunlight
 - nuclear meltdowns


 

 damming a river        