题目内容：
根据下面内容，回答题 In the late l960s．many people in North America turned their attention to environmental problems，and new steel-and-glass skyscraper,5 were widely criticized．Ecologists pointed out that acluster of tall buildings in a city often overburdens public transportation and parking lot capacities．
Skyscrapers are also lavish consumers，and wasters，of electric power．In one recent year．Theaddition of l7 million square feet of skyscraper omce space in New York City raised the peak daibdemand for electricity by l20，000 kilowatts--enough tO supply the entire city of Albany，New York，for a day．
Glass·walled skyscrapers can be especially wasteful．The heat loss(or gain)through a wall ofhalf-inch plate glass is more than ten times that through a typical masonry wall filled with insula．tion board．To lessen the strain on heating and airconditioning equipment，builders of skyscrapershave begun to use doubleglazed panels of glass，and reflective glasses coated with siNer or gold
mirror films that reduce glare aS well as heat gain．However，mirror-walled skyscrapers raise thetemperature of the surrounding air and affect neighboring buildings．
Skyscrapers put a severe strain on a city’S sanitation facilities，t00．If fully occupied，the twoWorld Trade Center towers in New York City would alone generate 2．25 million gallons of rawsewage each year--as much as a city the size of Stamford, Connecticut, which has a population ofmore than 109,000．
Skyscrapers also interfere with television reception, block bird flyways, and obstruct air traffic．
In Boston in the late 1960s, some people even feared that shadows from skyscrapers would kill thegrass on Boston Common．
Still, people continue to build skyscrapers for all the reasons that they have always builtthem-personal ambition, civic pride, and the desire of owners to have the largest possible amountof rentable space．
The main purpose of the passage is to( ) A．discuss the advantages and disadvantages of skyscrapers
B．compare skyscrapers with other modern structures
C．describe skyscrapers and their effect on the environment
D．illustrate various architectural
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