Skyscrs and Environment In the late 1960's，many people in North America turned their attention to environmental problems，and new steel-and-glass skyscrs were widely criticized. Ecologists pointed out that a cluster of tall buildings in a city often overburdens public transportation and parking lot capacities. Skyscrs are also lavish consumers，and wasters，of electric power. In one recent year，the addition of 17 million square feet of skyscr 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 skyscrs can be especially wasteful. The heat loss（or gain）through a wall of half-inch plate glass is more than ten times that through a typical masonry wall（砌筑墙）filled with insulation board（隔热板）.To lessen the strain on heating and air-conditioning equipment，builders of skyscrs have begun to use double-glazed panels of glass，and reflective glasses coated with silver or gold mirror films that reduce glare as well as heat gain. However，mirror-walled skyscrs raise the temperature of the surrounding air and affect neighboring buildings. Skyscrs put a severe strain on a city's sanitation facilities，too.If fully occeupied，the two World Trade Center 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. 【第11题】11.The main purpose of the passage is to_____.