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The gene comes in two versions, one of which is found in 99 per cent of Europeans. The other is found in 93 to 100 per cent of Africans, researchers at Pennsylvania State University report in the latest issue of Science. Scientists have changed the colour of a dark-striped zebrafish to uniform gold by inserting a version of the pigment(色素) gene into a young fish. As with humans, zebrafish skin colour is determined by pigment cells, which contain melanosomes(黑色素). The number, size and darkness of melanosomes per pigment cell determines skin colour. It appears that, like the golden zebrafish, light-skinned Europeans also have a mutation(变异) in the gene for melanosome production. This results in less pigmented skin. However, Keith Cheng, leader of the research team, points out that the mutation is dif ferent in human and zebrafish genes. Humans acquired dark skin in Africa about 1.5 million years ago to protect bodies from ultra-violet rays of the sun(太阳光紫外线), which can cause skin cancer. But when modern humans leave Africa to live in northern latitudes, they need more sunlight on their skin to produce vit amin D. So the related gene changes, according to Cheng. Asians have the same version of the gene as Africans, so they pr obably acquired their light skin through the action of some other gene that affects skin colour, said Cheng. The new discovery could lead to medical treatments for skin cancer. It also could lead to research into ways to change skin colour without damaging it like chemical treatment did on Michael Jackson. 54. The passage mainly tells us that ________. A. people can not change their skin colour without any pain B. the new discovery could lead to search into ways to change skin colour safely C. pop king Michael Jackson often changed his skin colour as he liked D. scientists have found out that people’s skin colour is determined by the gene 55. It can be inferred from the passage that ________. A. nowadays people who want to change their skin colour have to suffer a lot from the damage caused by the chemical treatment B. Europeans and Africans have the same gene C. the new discovery could help to find medical treatments for skin cancer D. there are two kinds of genes 56. Scientists have done an experiment on a dark-striped zebra fish in order to ________. A. find the different genes of humans’ B. prove the humans’ skin colour is determined by the pigment gene C. find out the reason why the Africans’ skin colour is dark D. find out the ways of changing peopl’s skin colour 57. The reason why Europeans are light-skinned is probably that ________. A. they are born light-skinned people B. light-skinned Europeans have mutation in the gen for melanosome production C. they have fewer activities outside D. they pay much attention to protecting their skin D The journey to the moon had been the first step toward future exploration(探险) in space. The distance between the Moon and Earth is very short indeed when compared with the distances between Earth and the other planets. Mars, the nearest planet to Earth is millions of miles away. Traveling to the planets will be man’s next aim. Such travels will be more challenging than the trip to the moon and certainly more adventurous. Recently, two American spaceships, Vikings 1 and 2, landed on Mars trying to discover whether that planet has any life on it. So far the signs of life on Mars has neither confirmed(确认) nor ruled out. Russians have discovered that the surface of Venus(金星) is so hot that it is almost certain that there is no life there. Also the atmosphere of Venus is extremely dense(稠) and the pressure is nearly a hundred times greater than that of the Earth’s atmosphere. Scientists believe man may find planets which have the same conditions as those we have on Earth , but man should realize Earth will be his only home for a long time and begin to love and care for it. 58. According to the passage, traveling to the planets will be ________. A. much easier and even more interesting B. far more exciting and dangerous C. man’s final aim D. man’s first step 59. Which of the following is Not true? A. Mars is nearer to the earth than the moon. B. The moon is much nearer to the earth than Mars. C. Of all the planets, Mars is the nearest to the earth. D. All the planets are much farther to the earth. 60. From the passage, we can guess_____. A. there is life on Mars B. there is no life on Mars C. the atmosphere of Mars is not so dense as that of Venus D. scientists will have little hope to find the answers 第二节(共5小题，每小题2分，满分10分) A.Christmas card. B.Jewelry. C.Pictures. D.Perfume. E.Holiday tickets. F.EBook reader. This Christmas, give something to your Mom that she’s going to cherish for a long time. Here are some of the best Christmas gifts for you to choose from and make this Christmas special for your mother. 61.__________ This is a gift which is truly suitable for women. Whenever you go for shopping for perfumes, just remember her personality and then choose. For more help you can refer to top perfumes for women 2010. 62.__________ (责任编辑：admin) |