题目

三块相同的金属平板A、B、D自上而下水平放置，间距分别为h和d，如图所示。A、B两板中心开孔，在A板的开孔上搁有一金属容器P，与A板接触良好，其内盛有导电液体。A板通过闭合的开关S与电动势为E0的电池的正极相连，B板与电池的负极相连并接地。容器P内的液体在在底部小孔O处形成质量为m、带电量为q的液滴后自由下落，穿过B板的开孔落在D板上，其电荷被D板吸收，液体随即蒸发，接着容器底部又形成相同的液滴自由下落，如此继续，设整个装置Britain’s seed bank, the only one in the world aiming to collect all of the planet’s wild plant species, has reached its goal of banking 10 percent by 2010.The Millennium Seed Bank Project, run by Kew Gardens—one of the oldest botanical gardens—will officially deposit the 24,200th species on Thursday, a pink, wild banana from China.More than 50 countries are now on board with Kew's giant task but vast places of the globe, including India and Brazil, still need to join in and donate seeds, director Paul Smith said.                                                                                                                                                            The seed bank is one of the largest and most diverse in the world with more than 1.5 billion seeds. Its goal is to help protect the planet’s bio-diversity during a time of climate change. The wild banana seed is under threat of extinction(灭绝) in southwest China from agricultural development. It is a vital food source for Asian elephants and important for growing bananas for human consumption.Stored at minus-20 degrees centigrade, so they can last for thousands of years, the seeds await the day that scientists hope never comes—when the species no longer exist in the wild.It is a race against time, Smith said, because in the last decade alone, 20 plants held in the bank have already been wiped out in the wild. He estimates that between a third and a quarter will become extinct this century."It is urgent and it is happening now. An area, the size of England, is cleared of primary vegetation（植被）every year." Smith said. Because most of the world's food and medicines come from nature, protecting wild plant species is quite important, scientists say. There are already many other seed banks safeguarding food crops, which only account for 0.6 percent of plant diversity.For Kew's next goal—to collect a quarter of wild varieties by 2020—the botanists need 10 million pounds a year, or a further 100 million pounds on top of the 40 million they have already been granted.小题1:What’s the final purpose of the Britain’s seed bank?A．To collect enough money for the project.B．To safeguard food crops.C．To protect wild plants from extinction.D．To help scientists study wild plants.小题2:The wild banana seed in China is in danger because of _______.A．the expanding of farming workB．the climate change in this areaC．the large number of Asian elephantsD．human’s large consumption小题3: We can learn from the passage that _______.A．the seeds in the bank can be used now and then all over the worldB．India and Brazil haven’t joined in the Seed Bank Project at present C．there is only one seed bank in the world at presentD．the wild plants in places like India and China will never die out小题4: What does the underlined word “it” in paragraph 7 refer to?A．The extinction of plant species.B．The Millennium Seed Bank Project.C．Britain’s seed bank.D．Kew Gardens’ next goal.小题5:Which of the following information isn’t mentioned in the passage?A．The global partnership of collecting wild plant species.B．The temperature condition of the conservative wild plant species.C．The government’s financial support for the seed bank project.D．Scientists’ concern on the extinct wild plant species.