题目内容
According to the passage, which of the following statements is true concerning teenagers in Europe？.
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Doctors and other scientists have concluded that ______ .
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 overburdens public transportation and parking tot capacities.
Skyscrapers are also lavish comsumers, 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 kilowattsenough to supply the entire city of Albany, New York, for a day.
Glass-walled skyscrapers can be especially wasteful. The beat loss (or gain) through a wall of half-inch plate glass is more than ten times that through a typical masonry wall filled with insulation 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 sih/er 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 Stanford, Connecticut, which has a population of more than 109,000. )
Skyscrapers also interfere with television reception, block bird flyways, and obstruct air traffic. In Bos ton 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--person al 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 ______.
The nuclear energy is released at the Sun’s center as high - energy gamma radiation, a form. of electro magnetic radiation like light and radio waves only of very much shorter wavelength. This gamma radiation is absorbed by atoms inside the Sun, to be reemitted at slightly longer wavelengths. This radiation, in its turn, is absorbed and reemitted. At the energy filters through the layers of the solar interior, it passes through the X - ray part of the spectrum, eventually becoming light. At this stage, it has reached what we call the solar sur face, and can escape into space, without being absorbed farther by solar atoms. A very small fraction of the Sun's light ,ma heat is emitted in such directions that, after passing unhindered through interplanetary space, it hits the Earth.
A simple magnifying glass, focusing the Sun’s rays, can scoarch, a piece of wood or set a Scrap of paper on fire. Solar radiation can also be concentrated on a much larger scale. It can burn a hole through thick steel plate, for example, or simulate the thermal shock of a nuclear blast. It can, that is, with the help of a super reflector of the sort that has been set up by French scientists high in the Pyreness. The world’s largest solar furnace is a complex of nearly 20,000 mirrors. It can concentrate enough sunlight to create temperatures in excess of 6000 degrees Fahrenheit.
The furnace’s appearance is as spectacular as its power. Its glittering eight - story - high reflector towers over very old houses. Anchored against a concrete office and laboratory building, the huge reflector consists of nearly 9000 separate mirrors. For the furnace to operate, these small mirrors must be adjusted so that their light will meet exactly at a focal point 59 feet in front of the giant reflector.
What does the passage mainly discuss？
It's important to remember that nutrients have to work ______, and to take too much of one
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