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. Ecologists pointing (21) that a cluster of tall buildings in a city often overburdens public transportation and parking lot (22) . Skyscrapers are also enormous (23) , and wasters, of electric power. In one recent year, the addition (24) 17 million square feet of skyscraper office space in New York City raised the (25) daily demand for electricity by 120,000 kilowatts-- enough to (26) the entire city of Albany for a day. Glass-wailed skyscraper can be especially (27) . The heat loss (or gain) through a wall of half-inch plate glass is more than ten times (28) through a typical masonry wall filled with insulation board. To lessen the strain (29) heating and air-conditioning equipment, (30) of skyscrapers have begun to use double-glazed panels of glass, and reflective glasses (31) with silver or gold mirror films that reduce (32) as well as heat gain. However, (33) skyscrapers raise the temperature of the surrounding air and (34) neighboring buildings. Skyscrapers put severe pressure on a city"s sanitation (35) , too. If fully occupied, the two World Trade Center towers in New York City would alone generate 2.25 million gallons of raw sewage each year--as (36) as a city the size of Stamford, Connecticut, which has a (37) of more than 109,000. Skyscrapers also (38) with television reception, block bird flyways, and obstruct air traffic. Still, people (39) to build skyscrapers for all the reasons that they have always built them--personal ambition and the (40) of owners to have the largest possible amount of rentable space.