Recently people have made great progress in using power of nature to produce electricity

问题补充：

Recently people have made great progress in using power of nature to produce electricity.

A. a; the

B. / ; /

C. the; /

D. a; an

答案：

A. a; the

B. / ; /

C. the; /

D. a; an

解析：解析：考查冠词。第一个空特指自然界的power，所以用定冠词；第二个空后的electricity是不可数名词，所以不用冠词。