--- What’re you going to do to protect the environment?

--- Plant trees on       side of the river.

A．both

B．all

C．each

D．every

 现代大型水电站是利用        能转化为         能的道理。拦河坝修得很高是用来提高上游水位，水位越         ，水的       能越大，水流下来转化成的           能越大。