题目

．科研人员测得—多肽链片段为“—甲硫氨酸—脯氨酸—苏氨酸—甘氨酸—缬氨酸—”，其密码子分别为：甲硫氨酸(AUG)、脯氨酸(CCU、CCC、CCA)、苏氨酸(ACU、ACC、ACA)、甘氨酸(GGU、GGA、GGG)、缬氨酸(GUU、GUC、GUA、GUG)。控制该多肽链合成的相应DNA片段为 根据以上材料，下列叙述正确的是                                   ( ) A．解旋酶作用于②处，使氢键断裂形成核糖核苷酸单链 B．基因突变只能发生在细胞分裂间期，因为DNA解旋形成单To hitch-hike successfully in any country you must be able to do two things: attract attention and at the same time convince the driver at a glance that you do not intend to rob or murder him. To fulfill the first requirement you must have some mark to distinguish you at once from all other hikers. A serviceman, for instance, should wear his uniform, a student his scarf. In a foreign country an unmistakable indication of your own nationality will also arrest a driver’s attention. When I hitch-hiked 9,500 miles across the United States and back recently I wore a well-tailored suit, a bowler hat and a trench coat, and carried a pencil-thin rolled black umbrella. My suitcase was decorated with British flags. Having plenty of luggage, moreover, I was not likely to be suspected of being a dangerous lunatic(精神病患者). I then had to get across to the driver the idea that I was a real traveler, and needed to get somewhere cheaply. But even with careful preparation, you must not assume that the task will be easy. You should be prepared to wait a little, for there are drivers who confess to a fierce prejudice against, （not to say hatred of）, hitch-hikers, and would no more pick up a hiker than march from Aldermaston to London. In America, my average wait was half-an-hour, and my longest two hours, but I have heard of people waiting all day; they probably took less pains to make themselves easy to notice. Nor must you assume that all the drivers who stop for you are nice, normal people. On one occasion I found myself driving with two boys of about nineteen who turned out to be on the run from the police, and were hoping to use me as an alibi. There are also lesser(较小的) risks: you may find yourself in the car of a Fascist fanatic, a Mormon missionary(传教士), or just a bad driver. You cannot tell, of course until you are in the car. But you soon learn the art of the quick excuse that gets you out again. If the hitch-hiker in the U.S. will remember that he is seeking the willingness of drivers to give him a free ride, and is prepared to give in exchange entertainment and company, and not go to sleep, he will come across the remarkable, almost legendary, hospitality of American of the West. It will also help if he can drive—I think that I drove myself about 4,500 of those 9,500 miles I hitch-hiked in the States. 56. A hitch-hiking serviceman should wear his uniform       .      A. so as not to look too unusual     B. to attract attention     C. to show he is on duty     D. to put the driver at ease 57. In paragraph 3, we learn that the writer      . A. has sometimes failed to hitch a ride B. has marched from Aldermaston to London C. has always been successful in hitching a ride D. has had to wait for long hours for a ride 58. The main idea of Paragraph 4 is that       . A. it is dangerous to be in a car with strangers B. hitch-hiking may turn out to be risky sometimes C. a hitch-hiker must also learn the art of quick excuse D hitch-hikers might come across bad drivers 59. In the last paragraph, the writer mainly wants to tell us that a hitchhiker should      . A. not talk to the driver too much B. fall asleep to make it a peaceful ride C. try to make himself pleasant and entertaining D. seek the willingness of drivers 60. A suitable title for the passage would be      .  A. “The Art of Hitch-hiking” B. “An Englishman’s View of the U.S.” C. “An English Hitch-hiker”      D. “The joys and Dangers of hitch-hiking