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结构中含有两个手性碳原子的为( )。
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Trillions of incredibly tiny diamonds, possibly formed by a dying star before the solar system was born 4.5 billion years ago, have been found by researchers (26) four meteorites. The powder-like diamonds could be among the oldest things in the (27) , said Roy Lewis, senior research associate at the University of Chicago. The diamonds may (28) clues about the chemistry of stars, and if scientists can determine how they formed, that could suggest better ways of manufacturing tiny diamonds for (29) purposes, he said. "It’s quite possible that nature is doing it more (30) than we’ve been doing it," he said. "So maybe we’ve got something to learn." The new find is (31) , said John Wood, staff scientist at the Harvard-Smithsonian Centre for Astrophysics. Although diamonds have been found before in meteorites, they were formed relatively recently (32) the shock of impact, he said in a telephone interview. But Wood said the new report made him "quite sure" the newly found diamonds are older than the sun. Lewis said researchers never expected to find diamonds when they started (33) a stone-like meteorite that had plunged into Mexican cornfield in 1969. They were studying an unusual carbon dust in the meteorite, and to purify the sample they went though several steps to dissolve other materials. They expected the sample to remain black through the purification, but to their surprise in the final step it turned (34) . Lewis said they believed the final stage had dissolved the carbon they wanted to study. But tests showed that the white residue was in fact made of carbon. Other tests found that it contained an unusual combination of forms of the gas xenon, (35) that it came from outside the solar system. Still another battery of tests (36) the residue as diamond dust, so fine that a row of 20,000 grains would extend about the (37) of a human hair. The researchers also found diamonds in three other meteorites, Lewis said. Tests showed all four meteorites were as old as the solar system, and that the embedded diamonds did not form within the meteorite (38) of collisions. So the diamonds must have (39) somewhere else before the meteorites formed, making them as old or older than the solar system. The diamonds may have formed in the upper atmosphere of a star in the late "red giant" stage, where the temperature and abundance of hydrogen could (40) diamonds to form as carbon gas condenses.
The British are the European Union’s worst linguists while the citizens of Luxembourg are the best, according to an EU poll published recently. Almost two-thirds of Britons know no language apart from their mother tongue, the highest figure recorded in the 15 EU countries. That compares to just 2.2 percent in Luxembourg, 12.3 percent of Danes and an EU average of 47.3 percent of people who speak no other language but their own, the poll of 16,000 Ell citizens said. But British travelers to Europe need not worry. English is the most common second language in the EU, spoken by 41 percent of the block’s citizens. In Denmark, Sweden and the Netherlands, at least 78 percent of people speak English as a second language. Although 47 percent of EU citizens know only their mother tongue, there is wide agreement that speaking foreign language is good thing. 72 percent of those polled believe foreign language skills are useful, 71 percent said everyone should know one foreign language and 69 percent said everyone should speak English. Which country has a percentage of 12.3 population that know no language apart from their mother tongue
Questions 11 to 13 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions. Now listen to the passage. How many high school students are presenting science projects in Portland this week
( )利用前药修饰原理，减少副作用。
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