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Passage FiveAlthough no one is certain why migration occurs, there are several theories. One theory is based upon the premise that prehistoric birds of the northen Hemisphere were forced south during the Ice Age, when glaciers covered large parts of Europe, Asia, and North America. As the glaciers melted, the birds came back to their homelands, spent the summer, and then went south again as the ice advanced in winter. In time, the migration became a habit, and now, although the glaciers have disappeared, the habit continues.Another theory proposes that the ancestral home of all modern birds was the tropics. When the region became overpopulated, many species were crowded north. During the summer, there was plenty of food, but during the winter, scarcity forced them to return to the tropics.A more recent theory, known as photoperiodism, suggests a relationship between increasing daylight and the stimulation of certain glands in the birds’ bodies that may prepare them for migration. One scientist has been able to cause midwinter migrations by exposing birds to artificial periods of daylight. He has concluded that changes occur in the bodies of birds due to seasonal changes in the length of daylight. The author states that birds left the tropics because （）
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Passage FourWhy is there no risk to the customer when a bank prints the customer’s name to his chequesWhen anyone opens a current account at a bank, he is lending the bank money, repayment of which he may demand at any time, either in cash or by drawing a check in favor of another person. Primarily, the bank-customer relationship is that of debtor and creditor who is which depending on whether the customer’s account is in credit or overdrawn. But, in addition to that basically simple concept, the bank and its customer owe a large number of obligations to one another. Many of these obligations can give rise to problems and complications but a bank customer, unlike, say, a buyer of goods, cannot complain that the law is loaded against him. The bank must obey its customer’s instructions, and not those of anyone else. When, for example, a customer first opens an account, he instructs the bank to debit (把……记入借方) his account only in respect of checks drawn by himself. He gives the bank specimens of his signature, and there is a very firm rule that the bank has no right or authority to pay out a customer’s money on a check on which its customer’s signature has been forged. It makes no difference that the forgery may have been a very skillful one: the bank must recognize its customer’s signature. For this reason there is no risk to the customer in the practice, adopted day banks, of printing the customer’s name on his checks, ff this facilitates forgery, it is the bank which will lose, not the customer. If someone forged your signature and drew money from your account （）
Passage TwoSome years ago industries had more freedom than they have now, and they did not need to be as careful as they must today. They did not need to worry a lot about the safety of the new products that they developed. They did not have to pay much attention to the health and safety of the people who worked for them. Often new products were dangerous for the people who used them; often conditions in the work place had very bad effects on the health of the workers.Of course sometimes there were real disasters which attracted the attention of governments and which showed need for changes. Also scientists who were doing research into the health of workers sometimes produced information which governments could not ignore. At such times, there were inquiries into the causes of the disaster or the problems. New safety rules were often introduced as a result of these inquiries; however, the new rule; came too late to protect the people who died or who became seriously ill.Today many governments have special departments which protect customers and workers. In the U.S., for example, there is a department which tests new airplanes and gives warnings about possible problems. It also makes the rules that aircraft producers must follow. Another department controls the foods and drugs that companies sell. A third department looks at the places where people work, and then reports any companies that are breaking laws which protect the health and safety of workers. Of course, new government departments and new laws cannot prevent every accident or illness, but they are having some good results. Our work places are safer and cleaner than before. The planes and cars which we use for travel are better. Producers are thinking more about the safety and health of the people who buy and use their products. It can be inferred from the passage that in the past（）
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