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Which type of waves does radar use？A．Sound.B．Heat.C．Radio.D．Light.
Which type of waves does radar use？
A．Sound.
B．Heat.
C．Radio.
D．Light.
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（请给出正确答案）
Which type of waves does radar use？
A．Sound.
B．Heat.
C．Radio.
D．Light.
答案
更多“Which type of waves does radar use？A．Sound.B．Heat.C．Radio.D．Light.”相关的问题
第1题
When We Are Asleep
Everyone dreams, but some people never recall their dreams, or do so very rarely. Other people always wake up with vivid recollections (记忆) of their dreams, though they forget them very quickly. In an average night of eight hours' sleep, an average adult will dream for around one hundred minutes, probably having three to five dreams, each lasting from ten to thirty minutes.
Scientists can detect when someone is having a dream by using an instrument which measures the electrical waves in the brain. During dreaming, these waves move more quickly. Breathing and pulse rate also increase, and there are rapid eye movements under the lids, just as though the dreamer were really looking at moving objects. These signs of dreaming have been detected in all mammals (哺乳动物) studied, including dogs, monkeys, cats, and elephants, and also some birds and reptiles (爬行动物). This period of sleep is called the “D” state for around 50% of their sleep; the period reduces to around 25% by the age of 10.
Dreams take the form. of stories, but they may be strange and with incidents not connected, which make little sense. Dreams are seldom without people in them and they are usually about people we know. One estimate says that two-thirds of the “cast” of our dream dramas are friends and relations. Vision seems an essential part of dreams, except for people blind from birth. Sound and touch are senses also often aroused, but smell and taste are not frequently involved. In “normal” dreams, the dreamer may be taking part, or be only an observer. But he or she cannot control what happens in the dream.
However, the dreamer does have control over one type of dream. This type of dream is called a “lucid”(清醒的) dream. Not everyone is a lucid dreamer. Some people are occasional lucid dreamers. Others can dream lucidly more or less all the time. In a lucid dream, the dreamer knows that he is dreaming.
Some people dream but cannot remember their dreams.
A．Right
B．Wrong
C．Not mentioned
第2题
阅读材料，回答题。
When We Are Asleep
Everyone dreams, but some people never recall their dreams, or do so very rarely. Other people always wake up with vivid recollections (记忆 ) of their dreams, though they forget them very quickly. In an average night of eight hours&39;sleep, an average adult will dream for around one hundred minutes, probably having three to five dreams, each lasting from ten to thirty minutes.
Scientists can detect when someone is having a dream by using an instrument which measures the electrical waves in the brain. During dreaming, these waves move more quickly. Breathing and pulse rate also increase, and there are rapid eye movements under the lids, just as though the dreamer were really looking at moving objects. These signs of dreaming have been detected in all mammals (哺乳动物) studied, including dogs, monkeys, cats, and elephants, and also some birds and reptiles (爬行动物) .This period of sleep is called the "D" state for around 50% of their sleep; the period reduces to around 25% by the age of 10.
Dreams take the form. of stories, but they may be strange and with incidents not connected, which make little sense. Dreams are seldom without people in them and they are usually about people we know. One estimate says that two-thirds of the "cast" of our dream dramas are friends and relations. Vision seems an essential part of dreams, except for people blind from birth. Sound and touch senses are also often aroused, but smell and taste are not frequently involved. In "normal" dreams, the dreamer may be taking part, or be only an observer. But he or she cannot control what happens in the dream.
However, the dreamer does have control over one type of dream. This type of dream is called a "lucid"(清醒的) dream. Not everyone is a lucid dreamer. Some people are occasional lucid dreamers. Others can dream lucidly more or less all the time. In a lucid dream, the dreamer knows that he is dreaming.
Some people dream but cannot remember their dreams. 查看材料
A.Right
B.Wrong
C.Not mentioned
第3题
The extent of the disaster in an earthquake depends on many factors. If you carefully build a toy house with an erect set, it will still stand no matter how much you shake the table. But if you build a toy house with a pack of cards, a slight shake of the table will make it fall. An earthquake in Agadir, Morocco, was not strong enough to be recorded on distant instruments, but it completely destroyed the city. Many stronger earthquakes have done comparatively little damage. If a building is well constructed and built on solid ground, it will resist an earthquake. Most deaths in earthquakes have been due to faulty building construction or poor building sites. A third and very serious factor is panic. When people rush out into narrow streets, more deaths will result.
The United Nations has played an important part in reducing the damage done by earthquakes. It has sent a team of experts to all countries known to be affected by earthquakes. Working with local geologists and engineers, the experts have studied the nature of the ground and the type of most practical building code for the local area. If followed, these suggestions will make disastrous earthquakes almost a thing of the past.
There is one type of earthquake disaster that little can be done about. This is the disaster caused by seismic (地震的) sea waves, or tsunamis. These are often called tidal (海潮的) waves, but the name is incorrect. They have nothing to do with tides.
In certain areas, earthquakes take place beneath the sea. These submarine earthquakes sometimes give rise to seismic sea waves. The waves are not noticeable out at sea because of their long wave length. But when they roll into harbors, they pile up into walls of water 6 to 60 feet high. The Japanese call them "tsunamis", meaning "harbor waves", because they reach a sizable height only in harbors.
Tsunamis (海啸) travel fairly slowly, at a speed of up to 500 miles an hour. An adequate warning system is in use to warn all shores likely to be reached by the waves.
But this only enables people to leave the threatened shores for higher ground. There is no way to stop the oncoming waves.
Which of the following CANNOT be concluded from the passage？
A．The number of earthquakes is closely related to depth.
B．Roughly the number of earthquakes varies much every year.
C．Earthquakes are most likely to occur within the upper 15 miles of the earth's surface.
D．Earthquakes are most likely to occur near the surfaces.
第4题
Which scientist first applied the theories of radio waves to practical devices？
A．Nikola Tesla.
B．Guglielmo Marconi.
C．Clerk Maxwell.
D．Heinrich Hertz.
第5题
Which of the following is not on the list of the countries hardest hit by the huge waves？
A．Indonesia.
B．Sri Lanka.
C．Malaysia.
D．Thailand.
第6题
Which of the following gives a general idea of how the noise killing system works？
A．By producing pressure waves going in the opposite direction.
B．By mixing high frequency sound waves with low frequency sound waves.
C．By mixing new sound waves with the noise and sending them out together.
D．By making copies of the unwanted sound waves and letting them out a little later.
第7题
Which of the following cannot explain why the interior of the earth is fluid？
A．There is great pressure at the centre.
B．Earthquake waves can move vertically.
C．The outer layer is made of rock.
D．The heat at the centre is too great.
第8题
Which of the following gives a general idea of how the noise-killing system works？
A．By producing pressure waves going in the opposite direction.
B．By mixing high frequency sound waves with low frequency sound waves.
C．By mixing new sound waves with the noise and sending them out together.
D．By making copies of tire unwanted sound waves and letting them out a little later.
第9题
Life on Other Planets
In 1961, scientists set up a gigantic, sensitive apparatus to collect radio waves from the far roaches of space, hoping to discover in them some mathematical pattern indicating that the waves were sent out by other intelligent beings. The first at tempt failed; but someday the experiment may succeed.
But is there intelligent life？ Life that has reached the stage of being able to send radio waves out-into space in a planned pattern？ Our own planet may have been in existence for five billion years and may have had life on it for two billion, but it is only in the last fifty years that intelligent life capable of sending radio waves into space has lived on earth. From this it might seem that even if there were no technical problems involved, the chance of receiving signals from any particular earth-type planet would be extremely small.
This does not mean that intelligent life at our level does not exist somewhere. There is such an unimaginable number of stars that, even with only a small chance, it seems certain that there are millions of intelligent life forms scattered through space. The only trouble is, none may be within hailing distance of us. Perhaps none ever will be; perhaps the huge distances that separate us from our fellow inhabitants of this universe will forever remain too great to be conquered. And yet it is conceivable that someday we may come across one of them or, frighteningly, one of them may come across us. What would they be bike, these extraterrestrial creatures？
Surely, it would seem, there is no way of telling. Here on earth alone, life has developed in many directions, taking on forms that could scarcely be invented by the wildest imagination if they were not already known to exist.
Who would dream that a mouse could fly if he had never seen a bat？ Who would predict blind lizards living in caves, or worms living in the intestines of other creatures？ Consider the giraffe, the humming-bird, the redwood tree, the Venus' flytrap, and see whether you can imagine any limit to various forms of life. Then how can anyone predict anything at all a bout extraterrestrial beings？
Ah, but all these variations and modifications that exist on earth are in some ways only superficial. In the chemist's test tube, all amazing differences in life forms vanish when we consider the basic similarity of those life forms, which is neither exciting nor amazing. Whatever appearance earth creatures may have, they are all made up of the same kinds of complex molecules; with minor variations, they all make use of the same chemical machinery.
For all its wonderful differences, life on earth is merely an imaginative variation on a single chemical structure. Life on any earthlike planet may prove to be similar.
As we understand life, it consists of molecules large enough and complex enough to meet the infinitely flexible requirements of living tissue. The molecules must be stable enough to retain their structure under some conditions, and unstable enough to change kaleidoscopically under other conditions. In living things on earth, the most important molecules of this type are the proteins, and as far as we know, nothing will substitute for them.
Furthermore, the changes these proteins undergo in the process of living can only take place against a watery back ground. Life began in the oceans, and even the various forms of land life are still from 50 to 80 percent water.
The chemical structure, then, upon which life is based, here and possibly on all earth-type planets, is protein-in water. If we are ever to meet up with creatures from an earth-type planet, we may not be able to predict their appearance, but we can predict that, whatever their shape, they will very likely be protein-in-water.
But what about life on planets that are not like the earth？ Wh
A．Y
B．N
C．NG
第10题
Her search for natural movement form. sent her to nature. She believed movement should be as natural as the swaying of the trees and the rolling waves of the sea, and should be in harmony with the movements of the Earth. Her great contributions are in three areas.
First, she began the expansion of the kinds of movements that could be used in dance. Before Duncan danced, ballet was the only type of dance performed in concert. In the ballet the feet and legs were emphasized, with virtuosity shown by complicated movements. Duncan performed dance by using all her body in the freest possible way. Her dance stemmed from her soul and spirit. She was one of the pioneers who broke tradition so others might be able to develop the art.
Her second contribution lies in dance costume. She discarded ballet shoes and stiff costumes. These were replaced with bare feet, and unbound hair. She believed in the natural body being allowed to move freely, and her dress displayed this ideal.
Her third contribution was in the use of music. In her performances she used the symphonies of great masters, including Beethoven and Wagner, which was not the usual custom.
She was as exciting and eccentric in her personal life as in her dance.
According to the passage, what did nature represent to Isadora Duncan？
A．Something to conquer.
B．A model for movement.
C．A place to find peace.
D．A symbol of disorder.
