阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项。

    With his unique black mane (鬃毛)and impressive stature(身材), 13-year-old Cecil was a popular tourist attraction at the 3.6 million-square-acre Hwange National Park(万基国家公园) in Zimbabwe (津巴布韦).

    Cecil was head of a pride of lions that includes 12 cubs(幼崽), but the well-known lion was shot and killed in early July by American dentist Walter J. Palmer.  

Cecil's death has already sparked an international outcry (强烈抗议) with many calling for an end to hunting endangered animals and for Palmer to be extradited(引渡) to Zimbabwe to stand trial.

Professor David Macdonald, the head of the Oxford University research program that monitored the daily movements of Cecil and dozens of other lions, is deeply saddened by Cecil's death. Macdonald hopes the death can inspire the public to take an interest in lion conservation.

    Macdonald says many of the lions tracked by the program have been shot  and killed. “The background to this story is that there is a crisis for lions throughout much of Africa.” He says.

    African lion populations have fallen almost 60 percent over the past thirty decades, and as few as 32,000 of them remain in the wild, according to the International Fund for Animal Welfare(国际爱护动物基金会).

“And as troubling as it is, the rarer these hunted animals become, the more hunter s are willing to pay to kill them,” said Jeff Flockedn, the fund's North American regional director.

    In addition to excessive hunting, lions throughout Africa also continue to face threats that include conflicts with local farmers, loss of habitat and risk of traffic and railway collisions(碰撞).

    Scientists are debating how to limit their newly-discovered power to change genetic structure (结构). Scientists already modify the genes (基因) of farm animals and agricultural plants to make them more productive or stronger. But now they can also change genes in wild animals and plants. These genes would continue into later generations. For example, it may be possible for scientists to remove from existence the kind of mosquitoes, small flying insects, that carry the Zika virus. They might also be able to permanently remove species (物种) of plants and animals that are damaging to other species.

    In a report published last week, the U. S. National Academies of Sciences, Engineering and Medicine (NAS) said it supports continued research on this kind of gene control. But it warned that it is not possible to know what will happen when these changed plants and animals are released (释放) into the wild.

    Sixteen biologists, ethicists (伦理学家) and policymakers are on an NAS committee that is examining the issue. They say that there is value to the new technology. But, they say, there is not enough evidence to support the release of modified organisms (生物体) from the laboratory into nature.

    Many people would support stopping mosquitoes and rats from carrying diseases. But scientists say we must understand the possible scientific, ethical, legal and social results of such action before we decide whether to take it. Gene modification is spread through reproduction (繁殖).

    Changed genes will continue to spread as long as an animal or plant continues to reproduce. They cannot be limited to a farm or kept within a country's borders. Scientists are wondering what may happen if a modified organism mates with another species. They are not yet sure how the modified genes would affect the other species. It is possible that those genes could harm those creatures or even lead to their disappearance from our planet.

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    One night in March 1999, a man was driving from California to Oregon, US, to visit some friends. He had stopped his car to have some food when he started to hear strange noises. Turning on the headlights, he saw an 8-foot-tall creature covered in thick, dark hair. The creature stared at him for a minute, turned in the road and walked off slowly into the woods.

    In the past 50 years alone, there have been thousands of reported sightings of similar creatures in the US, Canada, the Himalayas(喜马拉雅山地区)and even Hubei Province in China. The creature is known as bigfoot.

    Bigfoot is said to be a very tall(between 2 and 4. 5 metres), ape-like(类人猿似的)creature that is covered in hair and walks upright on two legs. It is very wary(警惕的)of human beings.

    Believers think bigfoot is a direct descendent(后代)of ancient gigantopithecus(巨猿). But it remains one of the planet's undiscovered secrets. There is a little evidence(证据)to support the believers' theory: traces of hair, footprints and body prints as well as the reported sightings. Some people have even showed what they say with photos or films of bigfoot.

    But so far, no one has found bones or any other definite proof that the giant creature exists.

    As a result many people believe the evidence is just part of a big trick.

    The footprints are easy to make and they say: all you need to do is to make two large feet out of plaster(石膏), attach them to the bottom of your shoes and walk with big steps. As for the photos and films, they are just people dressed in ape suits.

    They also say the sightings are not real, just people making mistakes. For example, bigfoot could be a bear living in the wild that sometimes stands up on its back legs.

    The fence was long and high. He put the brush into the whitewash and moved it along the top of the fence. He repeated the operation. He felt he could not continue and sat down.

    He knew that his friends would arrive soon with all kinds of interesting plans for the day.

    They would walk past him and laugh. They would make jokes about his having to work on a beautiful summer Saturday. The thought burned him like fire.

    He put his hand into his pockets and took out all that he owned. Perhaps he could find some way to pay someone to do the whitewashing for him. But there was nothing of value in his pockets—nothing that could buy even half an hour of freedom. So he put the bits of toys back into his pockets and gave up the idea.

    At this dark and hopeless moment, a wonderful idea came to him. It filled his mind with a great, bright light. Calmly he picked up the brush and started again to whitewash.

    While Tom was working, Ben Rogers appeared. Ben was eating an apple as he walked along the street. As he walked along it, he was making noises like the sound of a riverboat. First he shouted loudly, like a boat captain. Then he said “Ding－Dong－Dong”,“Ding－Dong－Dong” again and again, like the bell of a riverboat. And he made other strange noises. When he came close to Tom, he stopped.

    Tom went on whitewashing. He did not look at Ben. Ben stared a moment and then said: “Hello! I'm going swimming, but you can't go, can you？”

    No answer. Tom moved his brush carefully along the fence and looked at the result with the eye of an artist. Ben came nearer. Tom's mouth watered for the apple, but he kept on working.

    Ben said, “Hello, old fellow, you've got to work, hey？”

    Tom turned suddenly and said, “Why, it's you, Ben! I wasn't noticing.”

     “Say—I'm going swimming. Don't you wish you could? But of course you'd rather work—wouldn't you? Of course you would.”

    Tom looked at the boy a bit, and said, “What do you call work？”

     “Why, isn't that work？”

    Tom went back to his whitewashing, and answered carelessly.

     “Well, maybe it is, and maybe it isn't. All I know is, it suits Tom Sawyer.”

     “Oh come, now, you don't mean to say that you like it？”

    The brush continued to move.

     “Like it? Well, I don't see why I shouldn't like it. Does a boy get a chance to whitewash a fence every day？”

    Ben stopped eating his apple. Tom moved his brush back and forth, stepped back to look at the result, added a touch here and there, and stepped back again. Ben watched every move and got more and more interested. Soon he said，“Say, Tom, let me whitewash a little.”

    Tom thought for a moment, and was about to agree, but he changed his mind.

     “No—no—it won't do, Ben. You see, Aunt Polly wants this fence to be perfect. It has got to be done very carefully. I don't think there is one boy in a thousand, maybe two thousand, that can do it well enough.”

     “No—is that so? Oh come, now—let me just try. Only just a little.”

“Ben, I'd like to, but if it isn't done right, I'm afraid Aunt Polly ”

     “Oh, I'll be careful. Now let me try. Say—I'll give you the core of my apple.”

     “Well, here—No, Ben, now don't. I'm afraid …”

     “I'll give you all of it.”

    Tom gave up the brush with unwillingness on his face, but joy in his heart. And while Ben worked at the fence in the hot sun, Tom sat under a tree, eating the apple, and planning how to get more help. There were enough boys. Each one came to laugh, but remained to whitewash. By the time Ben was tired, Tom sold the next chance to Billy for a kite; and when Billy was tired, Johnny bought it for a dead rat—and so on, hour after hour. And when the middle of the afternoon came, Tom had won many treasures.

    And he had not worked. He had had a nice idle time all the time, with plenty of company, and the fence had been whitewashed three times. If he hadn't run out of whitewash, Tom would have owned everything belonging to his friends.

    He had discovered a great law of human action, namely, that in order to make a man or a boy want a thing, it is only necessary to make the thing difficult to get.

    William Butler Yeats, a most famous Irish writer, was born in Dublin on June 13, 1865. His childhood lacked the harmony that was typical of a happy family. Later, Yeats shocked his family by saying that he remembered "little of childhood but its pain". In fact, he inherited (继承) excellent taste in art from his family—both his father and his brother were painters. But he finally settled on literature, particularly drama and poetry.

    Yeats had strong faith in coming of new artistic movements. He set himself the fresh task in founding an Irish national theatre in the late 1890s. His early theatrical experiments, however, were not received favorably at the beginning. He didn't lose heart, and finally enjoyed success in his poetical drama.

    Compared with his dramatic works, Yeats's poems attract much admiring notice. The subject matter includes love, nature, history, time and aging. Though Yeats generally relied on very traditional forms, he brought modern sensibility to them. As his literary life progressed, his poetry grew finer and richer, which led him to worldwide recognition.

    He had not enjoyed a major public life since winning the Nobel Price in 1923. Yet, he continued writing almost to the end of his life. Had Yeats stopped writing at age 40, he would who probably now be valued as a minor poet, for there is no other example in literary history of a poet Auden wrote, among others, the following liners:

    Earth, receive an honored guest:

    William Yeats is laid to rest.

    Let the Irish vessel (船) lie

    Emptied of its poetry.

    Whales, like all mammals(哺乳动物),need air, and come to the surface to breathe through a blowhole. A drone(无人机)that floats over the blowholes of humpback whales as they are making annual journey along Australia's east coast is being used by Australian scientists for collecting nasal mucus(鼻腔粘液)of whales.

    Vanessa Pirotta, a biologist at Macquarie University says that nasal mucus indicates the health of the whale. "It is the biological mixture that you see as a whale takes a breath as it surfaces from the water," she said. You can hear sounds of sharp breaths as a whale breathes because, after all, they are animals like you and I. So as they take a breath it is a lot of lung bacteria coming out from their lungs, which we can collect to provide a brief idea of whale health.

    Australian researchers have attached a special dish that is used in scientific tests to a drone which flies through the whale's nasal mist. As a whale comes to take a breath—you can actually see it coming to the surface on really good weather days —the drone then lowers, the dish is then opened, collecting nasal mucus for later research.

    The research could help to solve one of the secrets of another impressive creature of the deep —the Southern right whale. Its numbers have recovered on Australia's west coast since hunting became suppressed but its population on the eastern seaboard remains stubbornly low.

    In the past, studies into whale health had to rely on examining whales that were either killed or those whales that had been trapped on a beach. Drones allow scientists to collect nasal mucus from free-swimming whales to gather information in a safe way.