单项选择题

The European Union countries were once worried that they would not have ______ supplies of petroleum.

A．proficient
B．efficient
C．potential
D．sufficient
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单项选择题
Even when textbooks are ______ through a school system, methods of teaching may vary greatly.
A．commonplace
B．standardized
C．competitive
D．generalized
单项选择题
There is a ______ difference in meaning between the words surroundings and environment .
A．gentle
B．subtle
C．feeble
D．humble
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