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肝-颈静脉回流征阳性，常见于（ ）。【2004年考试真题】
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诊断下肢大隐静脉曲张最可靠的依据是（ ）。【2003年考试真题】
Neither the Americans nor the Russians have the resources to continue human space flight on their own; both sides know they need each other. 61)It"s much easier and cheaper to get used to each other and to blend differing operating styles, languages, and systems on the aged Mir (a Russian word for "peace") than trying to do that while jointly building a new space station.NASA, in fact, calls its program of shuttle flights to Mir Phase 1 of the International Space Station (ISS). Phase 2 marks the beginning of actual construction. The procedures used to dock the shuttle to Mir, for example, also will be used as a lifeboat for the ISS. And Progress freighters, like the one that crashed into Mir in June" will haul cargo to the ISS. 62)One unintended benefit of Mir"s technical troubles is that they have actually forced the two nations to work much more closely together than they had planned.Except for a brief period in the 1970s with Skylab, NASA has never operated a space station; the Russians have been running them for years. Astronauts have long been trained intensively to perform specific tasks on shuttle flights lasting 18 days or less. 63)Russian astronauts, however, learn more general skills, since they spend many months in orbit and no one can forecast all the problems they might encounter.As a result of shuttle-Mir experience, NASA is revising astronaut training to include more of the general skills they will need on the ISS.NASA decided to send astronauts to Mir based on its long record of safe operation. But this year, crews aboard Mir have faced two of the most serious emergencies in the history of human space flight. 64)In February, an oxygen generator caught fire, shooting out 4-foot-long jets of flame like; fire extinguishers were bolted in place, delaying reaction to the fire.In June, a Progress Freighter collided with the Spektr module, puncturing it. Spektr had to be sealed off to prevent all the air from leaking from the spacecraft. 65)The ancient computer that controls Mir has failed many times, causing most other systems, including the one that keeps the station"s solar panels pointed at the sun, to shut down.One failure in August occurred while a Progress was docking. Last week, the computer crashed again, the carbon dioxide removal system shut down, and a mysterious brown fluid-probably rocket fuel—appeared to leak from the station.
In addition to the established energy sources such as gas, coal, oil and nuclear, there are a number of other sources that we ought to consider. Two of these are hydroelectric and tidal power.These two sources are 1 in that they are both renewable. 2 , hydropower is more widely used than tidal. In 3 , a substantial amount of electricity is already produced in HEP (hydroelectric power)stations worldwide, 4 tidal stations are still in the very early 5 of development.As far as geographical 6 is concerned, HEP projects are to be found on lakes and rivers. while tidal 7 are constructed only at river mouths where tidal 8 is great. Unfortunately these are 9 in number. At present HEP stations are found mainly in Norway, Canada, Sweden and Brazil, whereas tidal plants are in 10 in France, Russia and China.As regards capital 11 , both require very high investment. On the other hand, generating 12 are quite low in both cases. In fact, a large scale HEP plant is capable of producing power more 13 than conventional sources, such as coal, oil and nuclear plants. Tidal power also compares 14 with nuclear and oil generated electricity, 15 the amount of money on production. 16 HEP stations, tidal constructions have a long life 17 . It is estimated that they can operate for over 100 years. With respect to 18 of supply, tidal stations 19 from HEP ones in that they often can only supply power 20 . HEP stations, however, provide a constant supply of electricity.
In addition to the established energy sources such as gas, coal, oil and nuclear, there are a number of other sources that we ought to consider. Two of these are hydroelectric and tidal power.These two sources are 1 in that they are both renewable. 2 , hydropower is more widely used than tidal. In 3 , a substantial amount of electricity is already produced in HEP (hydroelectric power)stations worldwide, 4 tidal stations are still in the very early 5 of development.As far as geographical 6 is concerned, HEP projects are to be found on lakes and rivers. while tidal 7 are constructed only at river mouths where tidal 8 is great. Unfortunately these are 9 in number. At present HEP stations are found mainly in Norway, Canada, Sweden and Brazil, whereas tidal plants are in 10 in France, Russia and China.As regards capital 11 , both require very high investment. On the other hand, generating 12 are quite low in both cases. In fact, a large scale HEP plant is capable of producing power more 13 than conventional sources, such as coal, oil and nuclear plants. Tidal power also compares 14 with nuclear and oil generated electricity, 15 the amount of money on production. 16 HEP stations, tidal constructions have a long life 17 . It is estimated that they can operate for over 100 years. With respect to 18 of supply, tidal stations 19 from HEP ones in that they often can only supply power 20 . HEP stations, however, provide a constant supply of electricity.
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