题目内容
In 1870, horses and mules were the prime source of power on U. S. farms. One horse or mule was required to support four human beings—a ratio that remained almost constant for many decades. At that time, had a national commission been asked to forecast the horse and the population for 1970, its answer probably would have depended on whether its consultants were of an economic or technological turn of mind. Had they been "economists" , they would probably have projected the 1970 horse or mule population to be more than 50 million. Had they been "technologists", they would have recognized that the power of steam had already been harnessed to industry and to land and ocean transport. They would have recognized further that it would be the prime source of power on the farm. It would have been difficult for them to avoid the conclusion that the horse and mule population would decline rapidly.
According to the passage, what supplied most of the power on U. S. farms in 170？
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It can be inferred from the passage that by 170______.
The cowboy is the hero of many movies. He is, even today, a symbol of courage and adventure. But what was the life of the cowboy really like？
The cowboy's job is clear from the word cowboy. Cowboys were men who took care of cows and other cattle. The cattle were in the West and in Texas. People in the cities of the East wanted beef from these cattle. Trains could take the cattle east. But first the cattle had to get to the trains. Part of the cowboy's job was to take the cattle hundreds of miles to the railroad towns.
The trips were called cattle drives. A cattle drive usually took several months. Cowboys rode for sixteen hours a day. Because they rode so much, each cowboy brought along about eight horses. A cowboy changed horses several times each day.
The cowboys had to make sure that the cattle arrived safely. Before starting on a drive, the cowboys branded the cattle. They burned a mark on the cattle to show who they belonged to. But these marks didn't stop rustlers, or cattle thieves. Cowboys had to protect the cattle from rustlers. Rustlers made the dangerous trip even more dangerous.
Even though their work was very difficult and dangerous, cowboys did not earn much money. They were paid badly. Yet cowboys liked their way of life. They lived in a wild and open country. They lived a life of adventure and freedom.
A cowboy is a symbol of______.
Thousands of people in the city______to welcome the visiting guests.
Can animals be made to work for us？ Some scientists think that one day animals may be trained to do a number of simple jobs that are now done by human beings.
They point out that at a circus, for example, we may see elephants, monkeys, dogs and other animals doing quite skillful things. Perhaps you have seen them on the television or in a film. If you watch closely, you may notice that the trainer always gives the animal a piece of candy or a piece of fruit as a reward. The scientists say that many different animals may be trained to do a number of simple jobs if they know they will get a reward for doing them.
Of course, as we know, dogs can be used to guard a house, and soldiers in both old and modem times have used geese to give warning by making a lot of noise when a stranger or an enemy comes near. But it may be possible to train animals to work in factories. In Russia, for example, pigeons which are birds with good eyesight, are being used to watch out for faults in small steel balls that are being made in one factory. When the pigeon sees a ball which looks different from others, it touches a steel plate with its beak. This tums on a light to warn people in the factory. At the same time a few seeds are given as a reward. It takes three to five weeks to train a pigeon to do this and one pigeon can inspect 3 000 to 4 000 balls an hour.
Apes have been used in America in helping to make cars, and scientists believe that these large monkeys may be one day gather crops and even drive trains.
What made scientists think animal can be made to work for us one day？
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