单选题：根据下列内容，回答题。In the late 1960s, many people in North America t

根据下列内容，回答题。
In the late 1960s, many people in North America turned their attention to environmentalproblems, and new steel-and-glass skyscrapers were widely criticized. Ecologists pointed out that acluster of tall buildings in a city often transportation and parking lot capacities.
Skyscrapers are also lavish consumers, and wasters of electric power. In one recent year, theaddition of 17 million square feet of skyscraper office space in New York City raised the peak dailydemand for electricity by 120,000 kilowatts--enough to supply the entire city of Albany, NewYork, for a day.
Glass-walled skyscrapers can be especially wasteful. The heat loss (or gain) through a wall ofhalf-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 skyscrapershave begun to use double-glazed panels of glass, and reflective glasses coated with silver or goldmirror films that reduce glare as well as heat gain. However, mirror-walled skyscrapers raise thetemperature of the surrounding air and affect neighboring buildings.
Skyscrapers put a severe strain on a city's sanitation facilities, too. If fully occupied, the twoWorld Trade Center towers in New York City would alone generate 2.25 million gallons of rawsewage 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 traf-fic. In Boston in the late 1960s, some people even feared that shadows from skyscrapers would killthe grass on Boston Common.
Still, people continue to build skyscrapers for all the reasons that they have always builtthem--personal ambition, civic pride, and the desire of owners to have the largest possible amountof rentable space.
The main purpose of the passage is to__________. A．discuss the advantages and disadvantages of skyscrapers
B．compare skyscrapers with other modern structures
C．describe skyscrapers and their effect on the environment
D．illustrate various architectural