题目内容
telephones that it is hard to imagine what life would be like without them. When there is a power failure,
people grope about in flickering candlelight, cars hesitate in the streets because there are no traffic lights
to guide them, and food spoils in silent refrigerators.
Yet, people began to understand how electricity works only a little more than two centuries ago. Nature
has apparently been experimenting in this field for million of years. Scientists are discovering more and more
that the living world may hold many interesting secrets of electricity that could benefit humanity.
All living cells send out tiny pulses of electricity. As the heart beats, it sends out pulses of record; they
form an electrocardiogram, which a doctor can study to determine how well the heart is working. The brain,
too, sends our brain waves of electricity, which can be recorded in an electroencephalogram. The electric
currents generated by most living cells are extremely small,often so small that sensitive instruments are needed
to record them. But in some animals, certain muscle cells have become so specialized as electrical generators
that they do not work as muscle cells at all. When large numbers of these cells are linked together, the effects
can be astonishing.
The electric eel is an amazing storage battery. It can send a jolt of as much as eight hundred volts of
electricity through the water in which it lives. (An electric house current is only one hundred and twenty volts,
but two hundred and twenty volts in China.) As many as four-fifths of all the cells in the electric eel's body are
specialized for generating electricity, and the strength of the shock it can deliver corresponds roughly to length
of its body.
B. about 200 years ago
C. to be operating computers
D. by Thomse Edison
B. Electrical generators and animal muscle
C. Stones and dry wood
D. human brain and living cells
B. about one hundred and twenty volts
C. as high as the house current in China
D. stored in the water where it lives
B. we can always feel the electricity produced by living cells
C. human beings get their knowledge about electricity from nature
D. people learn about electricity from eels
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Advertising is a form of communication that uses all kinds of media, and is visible everywhere these days. Typical customers of advertising companies are other companies, or businessmen, who want to persuade potential customers to buy more of what they make or sell. But there are other kinds of customers. Some organizations spend large sums of money on advertising a political party or other group that sells what is not, strictly speaking, a product or service. Such non - profit organizations are not typical advertising customers, and they prefer ways of spreading knowledge, changing attitudes, and improving society. Many advertisements are designed to increase sales of products and services by either improving brand image or, in the case of non - profit organizations, expressing ideas. In order to achieve th~s, advertisements will often pass on truthful information while delivering their messages. Every major medium is a means of delivering these messages, including television, radio, cinema, magazines, newspapers, video games, the Internet and billboards (大幅广告牌). Advertising will usually be created and. placed by an advertising agency on behalf of company or other organization. Spending on advertising has increased greatly in recent years. In 2006, spending was estimated at $155 billion in the United States and $385 billion worldwide; the latter is expected to reach more than $500 billion by 2010. While advertising can be seen as a necessity for economic growth and social development, it is not without social costs. Advertisement emails and other forms of junk mail have become so popular that ~they have become a major burden to users of I nternet email services, as well as a financial burden on Internet email service providers.
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