As there is less and less coal and oil, scientists are exploring new ways of making use of energy, such as sunlight, wind and water for power and fuel.
A. primary
B. alternative
C. instant
D. unique
网友回答
A. primary
(答案→)B. alternative
C. instant
D. unique
解析：.
既然石油和煤都越来越少，人们只好使用一些其它可替代这些燃料的东西，alternative 有“可选择的，可替代的”之意，符合句意。primary“首要的，初期的”，instant“立即的，迅速的”，unique“独特的”。