单选题 Algae are plants that can
A． live in very hot temperatures
B． live in very cold temperatures
C． manufacture oxygen
D． all of the above
【答案】D。解析：由第三段的第一句“Sagan proposes that algae organisms，which can live in extremely hot or cold atmospheres and at the salne time produce oxygen”可知，A、B、C均正确，所以选D。
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2根据以下材料，回答题
In the late 1960s, many people in North America turned their attention to environmental problems, and new steel-and-glass skyscrapers were widely criticized. Ecologists pointed out that a cluster 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, the addition of 17 million square feet of skyscraper 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 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 skyscrapers 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 skyscrapers raise the temperature of the surrounding air and affect neighboring buildings.
Skyscrapers put a severe strain on a city's sanitation facilities, 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 much as a city the size of Stamford, Connecticut, which has a population of more 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 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.
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
