The European Union countries were once worried that they would not have ____ supplies of petroleum.
问题描述：
The European Union countries were once worried that they would not have ____ supplies of petroleum.
A) proficient B) efficient C) potential D) sufficient 为什么不能B 要选D
答
B efficient adj.有效率的,（直接）生效的,能干的
D sufficent adj.足够的,充足的；
因此D更符合语境.
翻译：欧盟国家曾经担心他们得不到足够的石油供应.