根据下面资料，回答题
Many people who fly at least occasionally have come down with a cold or the flu shortly after disembarking. Is the air in airborne commercial jets(21)_____? The Association of Flight Attendants (AFA), (22)_____which 42,000 flight attendants with 27 airlines are represented, evidently thinks so. The organization claims that the incidence of air-quality-related diseases has(23)_____among its members and demands that prompt actions be(24)_____to improve the conditions in the airplane cabin.
A study the AFA(25)_____in 1997 uncovered about 1,000 self-reported incidents of headaches,dizziness and memory loss(26)_____flight attendants and passengers. Some flight attendants were too ill to(27)_____ their safety duties, while others have been permanently disabled.
Because of airlines´ efforts to(28)_____ their expenses, cabin-air filters are not cleaned(29)_____
The complaints of flight attendants do not always give (30)_____to correct maintenance. Airlines turned to recycled air,(31)_____that they would reduce some of their costs. They are not required to put filters in. Airlines are(32)_____great pressure to get their flights out(33)_____ . So they do not pay as much attention to systems that are not as(34)_____ to flight schedule and safety.
Recent research findings emphasize the concern that filters can (35)_____engine chemicals into the cabin air. This may not happen(36)_____every flight, but it is a persistent problem.
In a study published in October 1998 an investigation was made (37)_____complaints of crew members(38)_____air quality and health. More than haft of the 200 subjects reported health problems they(39)_____to cabin air. It was concluded that these health problems were consistent with (40)_____harmful gases and substances.
第21题选