In the U.S., young people usually train as apprentices in .

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    Bats emit a very high frequency sound and listen for the echo that bounces off objects. The difference in time between emitting the sound and hearing the echo allows the bat to build up a mental “picture” of its environment. Homing pigeons can fly back to their home lofts by using the Earth’s magnetic field to navigate.

The animals with s___powers.

Since their first appearance on earth, men have gathered information and have attempted to pass useful ideas to other men. 46.The carving of word-pictures on the walls of ancient caves as well as hieroglyphics on stone tablets represent some of men's earliest efforts to convey information.Scenes of hunting, maps of battles, and the stories of heroes were put down for all to see.

But as civilizations grew more complex, better methods of communication were needed. The written word, carrier pigeons, the telegraph, andmany other devices carried ideas faster and faster from man to man. 47.In recent years one type of machine, the electronic computer, has become increasingly important in the lives of all the people in the industrialized nations of the world.Computers are now widely used aids for communication, calculation, and other activities. Their effect becomes more important every day.

Man has always been interested in extending the range of his senses and the power of his mind. Through the years, he has invented many instruments to help him see better and understand more. 48.The telescope, for example, was invented to allow him to look at faraway objects. To see the very small things in the world, the microscope was developed.Radio, telephone, and telegraph are means by which man has extended the range of his senses of hearing and speech.

While developing his power of thought, man first began to identify and count objects. He began to ask the questions “What is it?” and “How many?”. It was a long time ago that this numbering and comparing of things began.

49.New ways of helping with counting and recording information evolved. Marks of different kinds were taken to represent certain quantities, and other marks were taken to represent relationships between quantities.

New devices to aid in the manipulation of numbers were developed.

Electronic computers are among the fastest and most useful instruments for sorting and comparing in use today. 50.Computers provide the means for greater speed and accuracy in working with ideas than had previously been possible. With the development of these new tools, it is as if man has suddenly become a millionaire of the mind.

Although man has been growing mentally richer ever since he started to think, the electronic computer allows and will continue to allow him to perform tremendous “mental” tasks in a relatively short time. Great scientists of the past produced ideas which were the basis for great advances, but their ideas sometimes had to wait for years before they were understood sufficiently well to be of practical use. With the computer, the ideas of today’s scientists can be studied, tested, distributed, and used more rapidly than ever before.

51.Old lines and methods of communication do not work easily or efficiently with as much information as we have now. The repeated actions of preparing， sorting, filling, distributing, and keeping track of records and publications can be as troublesome as calculating. Errors occur because men grow tired and can be distracted.

The basic job of computers is the processing of information. For this reason computers can be defined as devices which accept information, perform mathematical or logical operations with the information, and then supply the results of these operations as new information.

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    Some air pollutants can cause cancer, problems with having children and other very serious illnesses as well as environmental damage. Air pollutants have killed people swiftly when large quantities were released; the 1984 release of methyl isocyanate at a pesticide-manufacturing plant in Bhopal, India, killed approximately 4,000 people and injured more than 200,000.

Air pollutants can be f__.

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   Studies have shown that people forced to share workspaces reported feeling marginalized, experienced more distractions, negative relationships and uncooperative behavior, not to mention feeling like their supervisors were being less supportive. Studies also find that open plan offices can have some negative psychological effects, reducing employee satisfaction, focus, and their feelings of having privacy at work.

Open office e___and its negative effects.

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Spinach may cause Alzheimer’s disease in at-risk people, research suggests. The salad leaf’s iron-rich content may damage the brain similar to how the compound causes metal to rust, according to the researchers. People with high levels of iron, which has previously been associated with Alzheimer’s, are more likely to experience rapid cognitive decline, a study found.

Iron-rich v   may lead to Alzheimer’s disease.

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    Driving for more than two hours a day negatively affects IQ levels, scientists have warned. In what might come as unwelcome news for middle-aged commuters, a recent study found that long periods behind the wheel could speed up the effects of age on the brain because the mind is less active on long car journeys.

Driving for a long t   may dull your mind.

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    Economists long ago point out why it is bad for a single firm to dominate a market. They believe that monopolists can set prices almost asthey please. Worse, if a company has no fear of competition, it needn’t worry too much about keeping customers happy and creating new and better products.

The c____of monopoly.

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  Recent research suggests that tea-producing areas in some places, notably East Africa, could decline by as much as 55 percent by 2050 as temperatures change. Tea pickers are also feeling the impacts of climate change. During harvest season, increased air temperatures are creating an increased risk of heatstroke for field workers.

The effect of r   temperatures on tea production.

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When you lose an hour of sleep, it decreases your well-being, productivity, health, and ability to think the following day. One of the most influential studies of human performance found that top performers slept 8 hours and 36 minutes per day. You are simply a different person when you operate on insufficient sleep.

Insufficient sleep may lead to p   performance.

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   Type D personalities usually have a low self-esteem and a great fear of disapproval. Negative emotions such as worrying, stress, depression and anger visit type D personalities more often. A small event that is usually overlooked by others can bother a type D a lot and even ruin his mood.

A c___type and its features.