You are presented with the quiz "Hydropower can devastate a what?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "hydropower requires damming a river" and "scientists agree that dams devastate rivers". So, what's the best answer to the question?

pick from the following.
(1). salmon;
(2). rocks;
(3). air;
(4). plants;
(5). soils;
(6). homes;
(7). river;
(8). habitat;
The answer is:
(7).