【文章內(nèi)容簡介】 all, you probably sing or whistle when you are happy.Some scientists believe that birds do sing some of the time just because they are happy. However, they sing most of the time for a very different reason. Their singing is actually a warning to other birds to stay out of their territory.Do you know what a “territory” is? A territory is an area that an animal, usually the male, claims as its own. Only he and his family are wele there. No other families of the same species are wele. Your yard and house are your territory where only your family and friends are wele. If a stranger should enter your territory and threaten you, you might shout. Probably this would be enough to frighten him away.If so, you have actually scared the stranger away without having to fight him. A bird does the same thing. But he expects an outsider almost any time, especially at nesting season. So he is screaming all the time, whether he can see an outsider or not. This screaming is what we call a bird’s song, and it is usually enough to keep an outsider away.Birds sing loudest in the spring when they are trying to attract a mate and warn others not to enter the territory of theirs.You can see that birds have a language all their own. Most of it has to do with attracting mates and setting up territories.50. According to the passage, most of the time birds’ singing is actually .A. an expression of happiness B. a way of warningC. an expression of anger D. a way of greeting51. What is a bird’s “territory”? A. A place where families of other species are not accepted. B. A place where a bird may shout at the top of its voice. C. An area for which birds fight against each other. D. An area which a bird considers to be its own.52. Why do birds keep on singing at nesting season? A. Because they want to invite more friends. B. Because their singing helps frighten outsiders away. C. Because they want to find outsiders around. D. Because their singing helps get rid of their fears.53. How does the writer explain birds’ singing? A. By paring birds with human beings. B. By reporting experiment results. C. By describing birds’ daily life. D. By telling a bird’s story.C Sirs, Your twelve thousand ‘Smart’ watches were received by our pany this morning. However, we wish to make a number of plaints concerning the serious delay in delivery and your failure to carry out our instructions regard to this order.It was firmly pointed out from the beginning that the delivery date had to be less than six weeks from the original order in order to satisfy our own customers’ requirements. While we understand that delays in production are occasionally unavoidable, we must point out that the major reason why the order was placed with your pany was that we were assured by you of its simplicity, and that your existing stocks were sufficiently high to ensure immediate shipment. Late delivery of the goods has caused us to disappoint several of our most valued customers, and will have an unfavorable effect on future orders.The second plaint concerns the difference in colour between the watches we ordered and those delivered. It was stated clearly in the order that watches in binations of green/purple and orange/purple only were required. However, only half the watches in the delivery received are of the colours specified. Our Hong Kong agent informed you of the importance of following our instructions exactly, since we consider there to be only a limited market in this country for watches of other colors at the present time. Any watches that are not of the specified colours will, of course, be returned to you.We are also somewhat concerned about the rather poor quality of the goods received, since it is obvious that the watches that finally arrived have been made from not good enough materials and have been produced to a lower standard than those in the sample. We have also found that a number of the watches do not appear to be working. Whether the latter problem is due to poor production, or damage in transportation is not yet clear, but we should like to point out that we feel this matter to be entirely your fault.As a result of the above problems, therefore, we feel that the most suitable course of action is to return to you unpaid any of the goods considered unsatisfactory. We shall also, of course, be forced to reconsider whether any further orders should be placed with your pany.We look forward to your early reply.Yours sincerely,John Smith54. The producers of ‘Smart’ watches were given the order because they promised_______.A. the designs were already preparedB. there was enough space for shipmentC. they could produce enough watches quicklyD. they had enough readymade watches to ship55. The last sentence of paragraph 5 “We shall also, of course, be forced to … with your pany” suggests that _______. A. the pany may stop trading with the watch manufacturers. B. the pany will probably reduce the number of watches to be ordered in the future. C. the writer is afraid their pany might go out of business soon. D. the pany i