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A．The earth will get even cooler.B．No species will survive in fifty years.C．30% of all
This remarkable technique is called thermography, and it has given human beings a new way of seeing. Thermography depends upon the fact that all objects give off infrared energy. The strength of these infrared emissions depends on the temperature of the body from which they come. Although scientists have long been able to measure the strength of infrared emissions, the problem was to turn these measurements into some sort of "picture".
Attempts were not notably successful until 1965, when Dr. Ray Lawson, of Montreal, made the first thermograms of the human body. Progress in the science has been rapid ever since, as industrial companies in Europe and the United States have come up with new developments.
Today's thermography looks, for the most part, like a small television camera. You point it at the subject, make a few fairly simple adjustments-and on an accompanying screen appear a black-and-white heat picture of the subject. Normally the warm areas are light, the cold areas dark, and the picture looks something like an ordinary photograph negative (底片). However, in some systems, black and white are reversed, and in still others the picture comes out in brilliant colors, with the various tones representing given temperatures.
Using one of these systems, experimenters made a picture of the past. Focusing on an empty chair after someone had been sitting in it for a few minutes; they were able to see the heat pattern left by the body, still emanating from the chair's fabric. The picture was so clear that they could detect that the sitter's legs had been crossed.
Thermography's most valuable use has been in the field of medicine. Already it has helped to save lives, and added to doctors' skills in treating disease. It has proved especially helpful in detecting breast tumors.
The standard examinations for breast cancer are mammography (X ray of the breast) and clinical examination. But, says Dr. Harold Izard, of Albert Einstein Medical Center in Philadelphia, who has used thermography to examine some 20,000 women for breast cancer, "The two methods do not catch everything. Thermography can indicate the possibility of some small cancers that have been missed. And it's safe and cheap. We can do a thermogram in a couple of minutes, and although the machines cost around $30,000 each, the price of operating them is a mater of pennies. And with the addition of thermography to the other two methods, we can get about 92 percent accuracy in detecting breast cancer."
What does the thermography depend on？
A．Because they can't be predicted.B．Because they happen very often.C．Because they kill
听力原文： Earthquakes are something that most people fear. There are some places that have few or no earthquakes. Most places in the world, however, have them regularly. Some places, like Iran and Guatemala have them frequently. Countries that have a lot of earthquakes are usually quite mountainous.
The most-talked-about earthquake in the United States was in San Francisco in 1909. Over 500 people died in it. The strongest one in North America was in 1964. It happened in Alaska.
Strong earthquakes are not always the ones that kill the most people. In 1755, one of the strongest earthquakes ever recorded was felt in Portugal. Around 20,000 people died.
In 1923, a very powerful earthquake hit the Tokyo-Yokohama area of Japan. A hundred and forty thousand people died. Most of them died in fires which followed the earthquake.
One of the worst earthquakes ever was in China in 1976. It killed a large number of people. The worst earthquake ever reported was also in China. 400,000 people were killed or injured in this quake, which happened in 1556.
Earthquakes are not the only acts of nature which people fear. Floods and tidal waves also cause people to be afraid. So do bad storms like typhoons and cyclones. Sometimes these things cause lots of deaths. In 1970, a cyclone and tidal wave killed over 200,000 in Pakistan.
These kinds of things make people afraid and they are very dangerous. But they probably do not worry people as much as earthquakes, especially in these modem times. The reason is that we often know they are coming, we have some warning. Someday we may be able to know an earthquake is coming. So far, however, no sure way is known to predict an earthquake. When one comes, it is a surprise. People cannot prepare for it.
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