题目内容
网络的几种拓扑结构中，在使用 (59) 时，各节点与中央单元进行连接，导致中央单元负荷重。
查看答案
搜索结果不匹配？点我反馈
更多问题
Is there enough oil beneath the Arctic National Wildlife Refuge (ANWR)to help secure America’s energy future President Bush certainly thinks so. He has argued that tapping ANWR’s oil would help ease California’s electricity crisis and provide a major boost to the country’s energy independence. But no one knows for sure how much crude oil lies buried beneath the frozen earth, with the last government survey, conducted in 1998, projecting output anywhere from 3 billion to 16 billion barrels. The oil industry goes with the high end of the range, which could equal as much as 10% of U.S. consumption for as long as six years. By pumping more than 1 million barrels a day from the reserve for the next two to three decades, lobbyists claim, the nation could cut back on imports equivalent to all shipments to the U.S. from Saudi Arabia. Sounds good. An oil boom would also mean a multibillion-dollar windfall(意外之才) in tax revenues, royalties (开采权使用费)and leasing fees for Alaska and the Federal Government. Best of all, advocates of drilling say, damage to the environment would be insignificant. "We’ve never had a documented case of an oil rig chasing deer out onto the pack ice," says Alaska State Representative Scott Ogan. Not so fast, say environmentalists. Sticking to the low end of government estimates, the National Resources Defense Council says there may be no more than 3.2 billion barrels of economically recoverable oil in the coastal plain of ANWR, a drop in the bucket that would do virtually nothing to ease America’s energy problems. And consumers would wait up to a decade to gain any benefits, because drilling could begin only after much bargaining over leases, environmental permits and regulatory review. As for ANWR’s impact on the California power crisis, environmentalists point out that oil is responsible for only 1% of the Golden State’s electricity output—and just 3% of the nation’s. What do the environmentalists mean by saying "Not so fast"(Line 1 ,Par
For more than thirty years after astronauts first set foot on the Moon, scientists have been unable to unravel the mystery of where the Earth’s only satellite came from. But now there is direct evidence that the Moon was born after a giant collision between the young Earth and another planet. Previous studies of rocks from the Earth and the Moon have been unable to distinguish between the two, suggesting that they formed from the same material. But this still left room for a number of theories explaining how—for example, that the Moon and Earth formed from the same material at the same time. It was even suggested that the early Earth spun so fast it formed a bulge that eventually broke off to form the Moon. Franck Poitrasson, and his colleagues at the Swiss Federal Institute of Technology have compared Moon rocks with rocks from Earth and discovered a surprising difference. They analysed the weight of the elements present in the rock using a highly accurate form of mass spectroscopy(光谱研究) that involves vaporising a sample by passing it through an argon (氩) flame. Although they appeared very similar in most respects, the Moon rocks had a higher ratio of iron-57 to iron-54 isotopes(同位素)than the Earth rocks. "The only way we could explain this difference is that the Moon and the Earth were partly vaporised during their formation," says Poitrasson. Only the popular "giant planetary impact" theory could generate the temperatures of more than 1700℃ needed to vaporise iron. In this scenario, a Mars-sized planet known as Theia crashed into Earth 50 million years after the birth of the Solar System. This catastrophic collision would have released 100 million times more energy than the impact believed to have wiped out the dinosaurs—enough to melt and vaporise a large portion of the Earth and completely destroy Theia. The debris from the collision would have been thrown into orbit around the Earth and eventually coalesced to form the Moon. When iron is vaporised, the lighter isotopes burn off first. And since the ejected debris that became the Moon would have been more thoroughly vaporised, it would have lost a greater proportion of its lighter iron isotopes than Earth did. This would explain the different ratios that Poitrasson has found. Previous studies could not distinguish between ______.
动员预付款扣回一般始于工程进度付款证书的累计金额超过合同价值的20%的当日，而止于合同竣工日期。 ( )
For more than thirty years after astronauts first set foot on the Moon, scientists have been unable to unravel the mystery of where the Earth’s only satellite came from. But now there is direct evidence that the Moon was born after a giant collision between the young Earth and another planet. Previous studies of rocks from the Earth and the Moon have been unable to distinguish between the two, suggesting that they formed from the same material. But this still left room for a number of theories explaining how—for example, that the Moon and Earth formed from the same material at the same time. It was even suggested that the early Earth spun so fast it formed a bulge that eventually broke off to form the Moon. Franck Poitrasson, and his colleagues at the Swiss Federal Institute of Technology have compared Moon rocks with rocks from Earth and discovered a surprising difference. They analysed the weight of the elements present in the rock using a highly accurate form of mass spectroscopy(光谱研究) that involves vaporising a sample by passing it through an argon (氩) flame. Although they appeared very similar in most respects, the Moon rocks had a higher ratio of iron-57 to iron-54 isotopes(同位素)than the Earth rocks. "The only way we could explain this difference is that the Moon and the Earth were partly vaporised during their formation," says Poitrasson. Only the popular "giant planetary impact" theory could generate the temperatures of more than 1700℃ needed to vaporise iron. In this scenario, a Mars-sized planet known as Theia crashed into Earth 50 million years after the birth of the Solar System. This catastrophic collision would have released 100 million times more energy than the impact believed to have wiped out the dinosaurs—enough to melt and vaporise a large portion of the Earth and completely destroy Theia. The debris from the collision would have been thrown into orbit around the Earth and eventually coalesced to form the Moon. When iron is vaporised, the lighter isotopes burn off first. And since the ejected debris that became the Moon would have been more thoroughly vaporised, it would have lost a greater proportion of its lighter iron isotopes than Earth did. This would explain the different ratios that Poitrasson has found. The main theme of the passage is ______.
微信支付 
支付宝支付