Read the following three passages．Each passage is followed by several questions or unfinished statements．For each of them there are four choices marked A, B, C and D．Choose the one that fits best according to the information given in the passage you have just read．

　　How the Grand Canyon was created remains one of the geology’s greatest mysteries．Some evidence suggests that the process was a gradual one in which the Colorado River(which runs through the canyon)slowly cut deeper and deeper into the ground over millions of years．But volcanic(火山的)rock samples taken from the canyon(峡谷)now suggest that the canyon was downcut instead．

　　Downcutting is when a flood of water rushes over a landscape with enough force to cut deeply into the ground and leaves behind a canyon．Such a flood is usually released when a natural or artificial dam bursts．

　　Robert Webb, a research geologist with U．S．Geological Survey, says natural dams seem to have formed and broken across the Colorado River several times during the last million years．The dams were built when lava(熔岩)from the eruptions(爆发)of nearby volcanoes flowed into the river．The lava hardened into hard rocks and blocked the river, causing it to back up and form a lake．Each time the lake grew so huge that it broke the rock dam, releasing a flash flood that furthered the downcutting process and deepened the canyon．The most recent dam break happened 165,000 years ago, says Webb, and released 15 million cubic(立方)feet of water per second．

　　Downcutting is not just an earthly event．Satellite photos sent back from Mars(a planet)suggest that the process has happened there, too, say researchers at the National Air and Space Museum．

　　The photos, taken by the Mars Global Surveyor, indicate that an enormous lake existed on Mars 3.5 billion years ago．The lake, which was big enough to flood Texas and California, eventually spilled into a large nearby hole．One edge of the hole broke, releasing a flash flood that quickly carved out a grand canyon about 2,100 meters deep and 885 kilometers long．Astronauts call the canyon MA’adim Vallis．

　　The existence of downcutting on Mars is just one more piece of evidence that the cold, dry planet was once warm and wet．

阅读理解

　　A soldier named John Blanchard struck up(建立)a pen pal friendship with a woman, Sally Maynell, who he had never met in the months before World War II．When the fighting began, their correspondence still continued．

　　Over the next year or so the two got to know each other through their letters．Even so, when Blanchard asked for a photograph, the woman refused．She felt that if he really cared, it wouldn’t matter what she looked like．

　　When the day finally came for him to return from Europe, they scheduled their first meeting－7∶00 pm at Grand Central Station in New York．“You’ll recognise me,” she wrote, “by the red rose I’ll be wearing on my suit．”

　　At the station a beautiful young woman approached him．She was wearing a green suit and was everything that he hoped Miss Maynell would be．But there was no red rose．There was another woman．She was well past 40 and had her hair tucked(塞)under a worn hat．She was more than plump, her fat feet thrust(挤)into shoes．Her pale face was gentle and her gray eyes had a warm twinkle(闪光)．On her coat, there was a red rose．

　　He did not hesitate．His fingers gripped the small worn copy of the book that was to identify him to her．“This will not be love, but it will be something precious, something perhaps even better than love, a feeling for which I have been and must ever be grateful．” he thought．

　　“I’m John Blanchard, and you must be Miss Maynell．I am so glad you could meet me．May I take you to dinner?” he asked．

　　The woman’s face broadened into a smile．“I don’t know what this is about, son．” she answered, “But the young lady in the green suit who just went by begged me to wear this rose on my coat．And she said if you were to ask me out to dinner, I should go and tell you that she is waiting for you in the big restaurant across the street．She said it was a kind of test!”

阅读理解

　　Children start out a natural scientists, eager to look into the world around them．Helping them enjoy science can be easy; there’s no need for a lot of scientific terms or expensive lab equipment．You only have to share your children’s curiosity．Firstly, listen to their questions．I once visited a seven-year-old classroom to talk about science as a job．The children asked me “textbook questions”about schooling, salary and whether I liked my job．When I finished answering, we sat facing one another in silence．Finally I said, “Now that we’ve finished with your lists, do you have questions of your own about science?”

　　After a long pause, a boy raised his hand, “Have you ever seen a grasshopper(蚱蜢)eat? When I try eating leaves like that, I get a stomachache．Why? ”

　　This began a set of questions that lasted nearly two hours．

　　Secondly, give them time to think．Studies over the past 30 years have shown that, after asking a question, adults typically wait only one second or less for an answer, no time for a child to think．When adults increase their “wait time” to three seconds or more, children give more logical, complete and creative answers．

　　Thirdly, watch your language．Once you have a child involved in a science discussion, don’t jump in with “That’s right” or “Very good”．These words work well when it comes to encouraging good behavior．But in talking about science, quick praise can signal that discussion is over．Instead, keep things going by saying, “That’s interesting” or “I’d never thought of it that way before”, or coming up with more questions or ideas．

　　Never push a child to “think”．It doesn’t make sense．Children are always thinking, without your telling them to．What’s more, this can turn a conversation into a performance．The child will try to find the answer you want, in as few words as possible, so that he will be a smaller target for your disagreement．

　　Lastly, show：don’t tell．Real-life impressions of nature are far more impressive than any lesson children can learn from a book or television program．Let children look at their fingertips through a magnifying glass(放大镜), and they’ll understand why you want them to wash before dinner．Rather than saying that water evaporates, set a pot of water to boil and let them watch the water level drop．