问题补充：
The scientists are trying to natural energy to decrease air pollution.
A. make friends with
B. make full use of
C. make notes of
D. make into
答案：
A. make friends with
(答案→)B. make full use of
C. make notes of
D. make into
解析：根据句意可知,特别是后面的natural energy to decrease air pollution, 这里选B,意思是:充分利用.
