[填空题]
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 62. ______.
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 63. ______.
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- 64. ______.
el, or insulation (隔音) from air
traffic noise may be provided by the purchasing 65.
______.
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,
66. ______.
consider the
