单选题 The European Union countries were once worried that they would not have supplies of petroleum.
A. pure B. efficient C. potential D. sufficient

【正确答案】 D

【答案解析】pure意为“纯的，纯粹的”；efficient意为“有效的，起作用的”；potential意为“潜在的，可能的”；sufficient意为“充足的，足够的”。所填之词修饰supplies，所以应选sufficient。