词汇与结构Mode S is ______ in controlled airspace in many countries.
A. possible
B. mandatory
C. indispensable
D. necessary
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词汇与结构Some countries have required that all aircraft ______ Mode S, even in uncontrolled airspace.
A. be equipped with
B. be equipped on
C. be equipped by
D. be equipped in
词汇与结构Secondary Surveillance Radar is referred to as “secondary”, to ______ it from the “primary radar”.
A. isolate
B. keep
C. separate
D. distinguish
词汇与结构Primary radar works by ______ bouncing a radio signal off the skin of the aircraft.
A. positively
B. passively
C. objectively
D. subjectively
词汇与结构Primary radar works best with large all-metal aircraft, but not so well on small, ______ aircraft.
A. composite
B. compound
C. compact
D. component