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设常数a＞0，讨论曲线y=ax与曲线y=2lnx的公共点的个数．
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July 21,2007 was a typical English summer’s day—it rained for 24 hours ! As usual, I rushed home from work at midday to check on the house. Nothing was amiss. By the time I left work at 5 pm, however, the road into our village was flooded. Our house had never been flooded, but as I opened the front door, a wave of water greeted me. Thank God the kids weren’t with me, because the house was 5 feet deep in water. We lost everything downstairs. And the plaster of the walls, ceilings pulled down.At first we tried to push on through. We didn’t want to move the children out of home, so we camped upstairs. We put a sheet of plastic across the floor to protect us from the damp. But after three months, we felt very sick, so we moved to a wooden house in a park. The house was small, but at first we were all just delighted to be in a new place. Unfortunately, things took longer than expected and we were there for 10 months. The life there was inconvenient. What surprised me most was how much I missed being part of a community. We had lived in a friendly village with good neighbors, and I’d never thought how much I’d miss that.Although our situation was very hard, it’s difficult to feel too sorry for yourself when you look at what’s happening elsewhere. I watched a news report about floods in Northern India and thought, "We didn’t have a straw but that was swept away, and our house is still standing. We’re lucky. "We moved back home in August. With December coming, there’s still reconstruction work to be done, so it’s difficult to prepare for Christmas. But I can’t wait—I’m going to throw a party for our friends in the village to say thanks for their support. This year, I won’t need any gifts—living away from home for months has made me realize how little we actually need or miss all our possessions. Although we are replacing things, there’s really no rush—we have our home back, and that’s the main thing. What does the author mainly want to express by telling her story（）
Our little boy came up to his mother in the kitchen one evening while she was fixing supper, and handed her a piece of paper that he had been writing on. After his morn dried her hands on an apron, she read it, and this is what it said: For cutting the grass $ 5.00 For cleaning up my room this week $ 1.00 For going to the store for you $ 0.50 Baby-sitting my kid brother while you went shopping $ 0.25 Taking out the garbage $ 1.00 For getting a good report card $ 5.00 For cleaning up and raking the yard $ 2.00 Total owed : $ 14.75 Well, I’ll tell you, his mother looked at him standing there expectantly, and boy, could I see the memories flashing through her mind. So she picked up the pen, turned over the paper he’d written on, and this is what she wrote: For the nine months I carried you while you were growing inside me, no charge. For all the nights that I’ve sat up with you, doctored and prayed for you, no charge. For all the trying times, and all the tears that you’ve caused through the years, there’s no charge. For all the nights that were filled with dread, and for the worries I knew were ahead, no charge. For the toys, food, clothes, and even wiping your nose, there’s no charge, son. When you ______, the cost of my love is no charge. Well, friends, when our son finished reading what his mother had written, there were great big old tears in his eyes, and he looked straight up at his mother and said: "Mom, I sure do love you. " And then he took the pen and in great big letters he wrote: "PAID IN FULL. " What do you learn after reading the passage (within 20 words)
Sustainable development is applied to just about everything from energy to clean water and economic growth, and as a result it has become difficult to question either the basic assumptions behind it or the way the concept is put to use. This is especially true in agriculture, where sustainable development is often taken as the sole measure of progress without a proper appreciation of historical and cultural perspectives.To start with, it is important to remember that the nature of agriculture has changed markedly throughout history, and will continue to do so. Medieval agriculture in northern Europe fed, clothed and sheltered a predominantly rural society with a much lower population density than it is today. It had minimal effect on biodiversity, and any pollution it caused was typically localized. In terms of energy use and the nutrients captured in the product it was relatively inefficient.Contrast this with farming since the start of the industrial revolution. Competition from overseas led farmers to specialize and increase yields. Throughout this period food became cheaper, safer and more reliable. However, these changes have also led to habitat loss.What’s more, demand for animal products in developing countries is growing so fast that meeting it will require an extra 300 million tons of grain a year by 2050. Yet the growth of cities and industry is reducing the amount of water available for agriculture in many regions.All this means that agriculture in the 21st century will have to be very different from how it was in the 20th. This will require radical thinking. For example, we need to move away from the idea that traditional practices are inevitably more sustainable than new ones. We also need to abandon the notion that agriculture can be "zero impact". The key will be to abandon the rather simple and static measures of sustainability, which centre on the need to maintain production without increasing damage. Instead we need a more dynamic interpretation, one that looks at the pros and cons of all the various ways land is used. There are many different agricultural performances besides food yield: energy use, environmental costs, water purity, carbon footprint and biodiversity. It is clear, for example, that the carbon of transporting tomatoes from Spain to the UK is less than that of producing them in the UK with additional heating and lighting. But we do not know whether lower carbon footprints will always be better for biodiversity. What is crucial is recognizing that sustainable agriculture is not just about sustainable food production. Specialization and the effort to increase yields have resulted in（）.
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