[判断题]

The acids in acid rain are the only reason that forms urban smog alone.

[填空题]The solution to acid rain can only come about ______.

[填空题]results in "Acid rain" 71. ______
is already the 2nd largest source of electricity in the U. S. 72. ______
may give off more radiative pollution into the air than a nuclear plant 73. ______
can be taken only when large enough collector plates are built 74. ______
is the cleanest practical source of electricity 75. ______
costs 30% less than coal-fired power in France 76. ______
is less easy to subject to shortages caused by strikes and natural disasters 77. ______
is less threatened by international crises 78. ______
will not be considered as a supplement to conventional electricity for several decades 79. ______
could contribute to global warming 80. ______
Our demand for electricity is climbing so fas

[单项选择] Researchers generally agree that acid rain arises primarily from the burning of coal and oil. The emissions contain oxides of nitrogen and sulfur, which can be carried hundreds of miles on the prevailing westernly winds. They eventually return to earth as dry gases and particulates and react with ground waters to form nitride or sulfuric acid. They may also be converted to the acids in the atmosphere by chemical processes that are still not fully understood. However the acids are formed, they have already been charged with a substantial list of damages. Corrosion of metal structures in windward areas of the country has been well-documented, but is a relatively minor entry on the list. Other forms of damage are far more insidious and longer-lasting. There is evidence, for example, that the acids leach heavy metals--aluminum, lead, and mercury-from the soil, which then poison plant roots and deprive them of vital nutrients. In lakes and rivers the acid alters the blood chemistry i
A. produced by air
B. emerged in the air
C. floating
D. polluting