Christmas bird – watching is popular in the U.S.A. When the holiday season comes, some Americans are likely to watch and count birds in the sky with great interest every day. This activity began in the early part of the last century. It has a one-hundred-year history. At that time, there was a so-called “holiday hunting” custom. In order to celebrate the holiday, the hunters went out to kill birds and beasts. By 1900, there were 27 bird lovers who decided to count birds instead of killing birds. Since then, Christmas bird-watching was held every year. It has been continued to the present. There were 42000 people who took part in the bird-watching last Christmas, from December 16 the year before to January 3 next year. They were in the United States and Canada, central America, south America and the Caribbean, watching and counting birds in the sky. The whole viewing area was divided into 1600 points. Each birdwatcher was responsible for 25 meters, and was required to write down the types and quantities of birds within 24 hours. A birdwatcher described what he had watched vividly in his diary—“ When I looked up, I saw a beautiful ‘landscape’ in the sky: Red-crowned cranes(丹顶鹤) were driving up in cunning wedges that split the air. They were so neatly arranged, coordinating their movements. I was excited and breathtaking. Interestingly, the “human” shape(人字行) always maintains 110° ” . “Why do red-crowned cranes choose to use ‘human’ shape when flying in formation?” He continued, “In my opinion, there are four reasons: first, the ‘human’ shape can make red-crowned cranes use increasing air which is produced by each other’s wings when they are swinging in the sky. It can increase the glide time and save physical ability. Second, the ‘human’ shape will enhance communication among the birds. The orders and the relevant information issued by the lead bird can be conveyed to each member in this migratory group unimpeded, accurately, rapidly and conveniently. Third, such a formation will help to find the birds left behind because of feeling run down as fast as possible, so that the young, the weak, the sick birds can get everyone’s help and encouragement. Finally, the ‘human’ shape shows not only beauty but also unity. It can give enemies a deterrent.They will be terrified and did not dare to attack the birds.The migration security of the birds will be ensured.” Environmental experts admired and evaluated Christmas bird-watching highly. They pointed out that it made perfect sense. On the one hand it could enhance the human awareness of environmental protection. On the other hand it could provide first-hand information on birds. 49．When did Christmas bird – watching begin? A．Sometime during Christmas holiday.         B．At the beginning of 20th century. C．In the early 19 th century.          D．Since there was Christmas Day 50．What do bird – watchers do when they are bird – watching? A．They kill birds and beasts.          B．They watch birds and beasts. C．They watch and count birds.     D．They look at the sky and write diaries. 51．The following are all reasons for red – crowned cranes flying in “human” shape except      . A．they can help each other and ensure their safety B．they can communicate with each other in order to reduce tiredness. C．they can make use of the air produced by each other’s wings. D．they can look stronger in case they come across enemies 52．This passage consists of five paragraphs. Please arrange the five main ideas of the paragraphs in order of their appearance in the passage. a. How the bird – watchers divided their watching task and what was done. b. How Christmas bird – watching came into being. c. Christmas bird – watching is of great importance environmentally and scientifically. d. A Christmas bird – watcher watched and was amazed by red – crowned cranes. e. Red – crowned cranes fly in “human” formation for quite good reasons. A．a – b – c – d – e         B．b – c – e – d – a         C．b- a – d – e – c D．b – d – e – a – c