填空题.The economic costs of noise are several. Airports are currently operating at less than 1 because of noise regulations which restrict their hours of operation. For instance, at Washington's National Airport no jet traffic is allowed from 11 p.m. to 7 a.m. Other airports restrict the use of certain runway. One estimate is that noise 2 reduce possible airport use by 20 percent. The 3 cargo trade is especially affected by night restrictions. In the case of airports, jet engines may be 4 to reduce their noise level, or insulation from air traffic noise may be provided by the purchase of land around airports or the insulation of buildings. One estimate is that $5.7 billion would be required to 5 all existing jet engines with noise control devices. However, 6 the current state of the art, even taking this step will not reduce noise levels at all points to 7 values. Some combination of methods is probably necessary. If all aircraft were made quieter by existing methods, there would be a number of economic benefits. An increase in airport capacity would 8 . Property values near airports might rise. Transportation costs to and from airports could be reduced since the airports now could be located closer to population center. Much research still needs to be done on the economic 9 of noise reduction and noise effects. Although some of the effects of noise pollution are known, more must be discovered about its effects on health, productivity, property values and the quality of life. 10 , the cost of noise pollution control to the economy as a whole needs to be investigated. A. identification B. equip C. profitable D. capacity E. pollution F. restrictions G. transformed H. significant I. furthermore J. acceptable K. modified L. accordingly M. considering N. occur O. aspects