单选题
In the late 1960's, many people in North America turned their attention to environmental problems, and new steel-and-glass skyscrapers were widely criticized. Ecologist pointed out that a cluster of tall buildings in a city often overburdens public transportation and parking lot capabilities. Skyscrapers also lavish consumers, and wasters, of electric power. In one recent year, the addition of 17 million square feet of skyscraper office space in New York City raised the peak daily demand for electricity by 120,000 kilowatts — enough to supply the entire city of Albany, New York, for a day. Glass-walled skyscrapers can be especially wasteful. The heat loss through a wall of half-inch plate glass is more than ten times that through a typical masonry wall filled with insulation board. To lessen the strain on heating and air-conditioning equipment, builders of skyscrapers have begun to use double-blazed panel of glass, and reflective glasses coasted with silver or gold mirror films that reduce glare as well as heat gain. However, mirror-walled skyscrapers raise the temperature of the surrounding air and affect neighboring buildings. Skyscrapers put a sever strain on the city's sanitation facilities, too. If fully occupied, the two World Trade Towers in New York city would alone generate 2. 25 million gallons of raw sewage each year as much as a city the size of Stanford, Connecticut, which has a population of more than 109,000. Skyscrapers also interfere with the television reception, block bird flyways, and obstruct the traffic. In Boston in the late 1960's, some people even feared that shadows from skyscrapers would kill the grass on Boston Common. Still, people continue to build skyscrapers for all the reasons they have always built them personal ambitions, civic pride and the desire of owners to have the largest possible amount of retable space.