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Passage 28 In every day usage "hot" means "having a lot of heat". Many people think that "cold" is something completely separated from heat. But this is not true. "Cold" simply means "having very little heat." Your life depends on heat. In fact, every living thing depends on it. (28) Without heat, every living thing would be frozen to death. All living things get their heat from the sun, which provides the conditions in which life is possible. Since the dawn of history, man has been able to make his own heat. He has been able to release the sun’s heat that is trapped in things such as wood, coal and oil. And he has been able to use this heat. Heat has made civilization possible. With heat, man could melt metals. As man learned to use metals and fuels, industries grew. As a result, engines were invented. These are machines that change heat energy into mechanical energy. Engine can do the work of many men. Without engines industrial civilization is impossible. Yet when the first engines were built in the 17th century, men were still wondering about the nature of heat. "What is it" they asked. Not until the early years of 19th century did they find the right answer. From the sentence "he has been able to release the sun’s heat that is trapped in things such as wood, coal and oil" we know______.
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Passage 38 Animals do many useful and entertaining jobs. (38) Dogs are particularly valuable in guiding the blind (a trained dog can learn never to cross a busy street when cars are coming, even if his master commands him to do so), protecting property, finding lost people, and hunting criminals. Horses are used in guarding herds, carrying men in lands where there are no roads, and helping farmers plow fields. Pigeons have long been used to carry message. Wild animals from the jungles, forests and seas are very popular performers in circuses and movies. People realize that, although animals may not have the same intelligence as human beings, they are smart enough to learn certain things. The first thing a dog is taught is to obey. It should not take too long for him to learn commands. Simple orders, such as "sit, lie down, stay there, come here" can even be taught by a child. Training a dog to be a watchdog often produces unexpected results. Some dogs quickly learn the difference between unwanted people and friends. This is because their masters welcome friends and invite them into their houses. However, some dogs will always attack the postmen who come to deliver letters. One explanation for this behavior is that, although the postman comes to the house frequently, he never enters the house. Therefore, the dog thinks the postman is someone who is not wanted, but keeps coming back anyway. Masters of dogs who attack postmen can easily show the dogs that the postman is a friend and the dog does not need to treat him as an unwanted person. A dog is quite ready to do what his master wishes. And a dog is always happy when he is praised for proper understanding. Dogs who accompany blind people must learn______.
Passage 37 Why don’t birds get lost on their long flights from one place to another Scientists have been puzzled over this question for many years. Now they’re beginning to fill in the blanks. Not long ago, experiments showed that birds rely on the sun to guide them during daylight hours. But what about birds that fly by night (37) Tests with artificial stars have proved that certain night-flying birds are able to follow the stars in their long-distance flights. A dove had spent its lifetime in a cage and had never flown under a natural sky. Yet it showed an inborn ability to use the stars for guidance. The bird’s cage was placed under an artificial star-filled sky. The bird tried to fly in the same direction as that taken by his outdoor cousins. Any change in the position of the artificial stars caused a change in the direction of his flight. The stars are apparently their principal means of navigation. When the stars are hidden by clouds, they seemingly find their way by such landmarks as mountain ranges, coast lines, and river courses. But when it’s too dark to see these, the doves circle helplessly, unable to find their way. The reason why birds don’t get lost on long flights______.
Passage 43 Sometimes it is impossible to send all the mail that arrives at the post office. Perhaps there is an inadequate or illegible address and there is no return address. The post office cannot just throw the mail away, so it becomes "dead mail". Dead mail is then sent to one of the U.S. Postal Service’s dead mail offices in Atlanta, New York, Philadelphia, St. Paul, and San Francisco. Seventy-five million pieces of mail can end up in these offices in one year. The staff ’of the dead mail offices has different ways to deal with all of these pieces of dead mail. First of all, they look for clues that can help them deliver the mail; they open packages in the hope that something inside will show where the package came from or is going to. (43) Dead mail will also be listed on a computer so that people can call in and cheek to see if a missing item is there. However, all of the mail cannot simply be stored forever: there is just too much of it. When a lot of dead mail has piled up, the dead mail offices hold public auctions. Every three months, the public is invited to the offices and containing items found in dead mail packages are sold to the highest bidder (出价人). Which is the best title for the passage
Passage 29 The first English window was just a slit in the wall. (29) It was cut long, so that it would let in as much light as possible, and narrow, to keep out the bad weather. However, the slit let in more wind than light. This is why it was called "the wind’s eye". The word window itself comes from two Old Norse words for wind and eye. Before windows were used, the ancient halls and castles of northern Europe and Britain were dark and smoky. Their great rooms were high, with only a hole in the roof to let out the smoke from torches and cooking fires. As time went on, people wanted more light and air in their homes. They made the wind’s eyes wider so as to admit air and light. They stretched canvas across them to keep out the weather. The underlined word "canvas" probably means______.
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