Skyscrs andEnvironment

In the late 1960's,many people in North America turned their attentionto environmental problems,and new steel-and-glass skysc.rs were widelycriticized.Ecologists pointed out that a cluster of tall buildings in a cityoften overburdens public transportation and parking lot capacities.

Skyscrs are also lavish consumers,and wasters,of electric power.Inone recent year,the addition of 17 million square feet of skyscr officespace in New York City raised the peak claily de-

mand for electricity by 120,000kilowatts-enough to supply the entire city of Albany,New York,for a day.

Glass-walled skyscrs can be especially wasteful.The heat loss (orgain) through a wall of half-inch plateglass is more than ten times that through a typical masonry wall(彻筑墙) filled with insulation board(隔热板) .Tolessen the strain on heating and air-conditioning equipment,builders ofskyscrs have begun to use double-glazed panels of glass,and reflectiveglasses coated with silver or gold mi.rror films that reduce glare as well asheat gain.However,mirror-walled skyscrs raise the temperature of thesurrouncling air and affect neighboring buildings.

Skyscrs put a severe strain on a city's sanitation facilities ,too.If fully occupied , the two World Trade Center towers in New York Citywould alone generate 2.25 million gallons of raw sewage each year-as much as acity the size of Stanford, Connecticut,which has a population of more than109,000.

11. The main purpose of the passage is to __________.