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．The addition of l7 million square feet of skyscraper omce space in New York City raised the peak daib demand 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 of half-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 air conditioning equipment，builders of skyscrapers have begun to use double glazed 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 the temperature of the surrounding air and affect neighboring buildings． Skyscrapers put a severe strain on a city’S sanitation facilities，t00．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 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 the grass on Boston Common． Still, people continue to build skyscrapers for all the reasons that they have always built them-personal ambition, civic pride, and the desire of owners to have the largest possible amount of rentable space． According to the passage, what is one disadvantage of skyscrapers that have mirrored walls? ( )
A. The exterior surrounding air is heated． B. The building materials are very expensive． C. Construction time is increased． D. Extra air-conditioning equipment is needed