The amount of _____ that drains into rivers and streams in a geographic area determines the amount of water available for producing hydropower.

Hydropower systems build pressure either by containing the water behind a dam, or within a pipe that runs down a hill. The weight of the water behind the dam or in the pipe creates pressure at the bottom. More height creates more pressure, and more pressu

According to different operation methods, reservoir operation can be divided into： A: conventional reservoir operation and optimal reservoir operation B: flood control operation, hydropower generation operation, comprehensive operation C: long-term operation, short-term operation, real-time operation D: single reservoir operation and multiple reservoir operation

‏Each pair of sentences contains a main idea statement and a supporting detail from the same paragraph. Decide which sentence states a main idea in each pair.‍ A: Green energy technologies play much less of a role. B: Hydropower, at 7 percent of national electrical generating capacity, is an important contributor; unfortunately, potential growth is very limited. C: / D: /