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  3. The economic costs of noise to society are several. Airports are currently op- erating at less than capacity because of noise re

The economic costs of noise to society are several. Airports are currently op- erating at less than capacity because of noise re

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问题    The economic costs of noise to society are several. Airports are currently op-
erating at less than capacity because of noise regulations, which restrict their      【S1】______.
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 run-
ways. One estimated is that noise restrictions reduce possible airport use by 20      【S2】______.
percent. The profitable cargo trade is especially affected by night restrictions.
   In the case of airports, jet engines may be modifying to reduce their noise lev-   【S3】______.
el, or insulation (隔音) from air traffic noise may be provided by the purchasing     【S4】______.
of land around airports. It is estimated that $ 5.7 billion would be required to
equip all existing jet engines for noise control devices. However,                    【S5】______.
consider the current state of the art, even taking this step will not reduce noise    【S6】______.
levels at all points to acceptable values. Some combination of methods is proba-
bly necessary.
   If all aircraft are made quieter by existing methods, there would be a number      【S7】______.
of economic benefits. An increase in airport capacity would occur. Property val-
ues near airports might rise. Transportation costs to and from airports could be
increased since the airports now could be located closer to population centers.       【S8】______.
   Much research still needs to be done on the economic aspects of noise re-
duction and noise effects. Although some of the effects of noise pollution are
known, more must be discovered about their effects on health, productivity, prop-     【S9】______.
erty values and the quality of life. Furthermore. the cost of noise pollution to the
economy as a whole needs to be investigated.
   The public must be alert about the dangers and economic costs of noise poi-        【S10】______.
lution so that people may make intelligent choices and exert appropriate pres-
sures.
【S7】
选项
答案are→were
解析 语气误用。本句为if引导的虚拟语气，从句应当用过去式，表示跟现在的事实相反。
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