题目内容
The high _____ of people on large airliners provides an alluring target for terrorism.
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Eating establishments have started using plastic glasses _____ glasses made out of glass to reduce the usefulness of such items as weapons.
Passengers usually will not have to be re-screened if ______ from a domestic flight.
The freight is ready for _____.
Taxi operations require constant _____ by the entire flight crew, not just the pilot taxiing the airplane.
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