单项选择题

It has taken many years to adopt internationally recognized standards for the licensing of aircraft pilots.

A. data
B. criteria
C. committees
D. flags
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单项选择题
The trumpet was part of the opera orchestra long before it became a standard orchestral instrument.
A. major
B. tuneful
C. desirable
D. regular
单项选择题
United States Navy Admiral Alfred Mahan wrote many books on naval strategy and sea power.
A. tactics
B. history
C. battles
D. armaments
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