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试述抵销须具备的要件。
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Aristotle believed that the heavens were perfect. If they ever were, they are no longer. The skies above Earth are now littered with the debris (残骸) of dead satellites, bits of old rockets and the odd tool dropped by a spacewalking astronaut. Such is the extent of the detritus that the first accidental collision between two satellites has already taken place. It happened in February 2009, when a defunct (废弃的) Russian Cosmos smashed into a functioning American Iridium, destroying both and creating even more space junk. To stop this sort of thing happening again Vaios Lappas of the University of Surrey, in England, has designed a system that will remove satellites from orbit at the end of their useful lives--and as a bonus will scour part of the sky clean as it does so. Dr. Lappas’s satellite-removal system employs a solar sail. As light from the sun hits the sail, it imparts a minuscule but continuous acceleration. When a satellite is first launched, the sail is angled in a way that causes this acceleration to keep the satellite in orbit. (Orbits gradually decay as a result of collisions with the small number of air molecules found even at altitudes normally classified as "outer space". ) Solar sails have yet to be used widely to propel spacecraft in this way--several earlier versions came unstuck when the sails failed to unfurl properly-but doing so is not a novel idea in principle The novelty Dr. Lappas envisages is to change the angle of the sail when the satellite has become defunct. Instead of keeping the derelict craft in orbit, it will, over the course of a couple of years, drag it into the atmosphere and thus to a fiery end. Not only that, but the sail will also act like a handkerchief, mopping up microscopic orbital detritus such as flecks of paint from previous launches. A fleck of paint may not sound dangerous, but if travelling at 27 000kph (17 000mph), as it would be in orbit, it could easily penetrate an astronaut’s spacesuit. A prototype of Dr. Lappas’s design, called CubeSail, will be launched late next year. It weighs just 3kg and, when folded up, measures 30cm (12 inches) by 10era by 10era. Once unfurled, however, the sail will have an area of 25 square metres. If this prototype, which is paid for by EADS, a European aerospace company, proves successful, solar sails might be added to many future satellites. That would enable them to be removed rapidly from orbit when they became useless and would restore to the skies some measure of Aristotelian perfection. The first sentence in this passage is to ______.
患者，35岁，上腹部不适5年，伴有腹胀及腹痛，腹部无压痛、反跳痛及肌紧张。多在进食后出现，行胃镜检查诊断为胃溃疡，Hp(+)。 幽门螺杆菌的根除方案是
某豆油厂与某粮油公司于1999年6月2日订立了一份大豆买卖合同，合同约定，粮油公司于同年8月底之前向豆油厂提供大豆10吨，豆油厂于9月1。日向粮油公司支付货款1.6万元。合同订立后不久，双方又订立了一份豆油买卖合同，合同约定，豆油厂于同年7月底向粮油公司提供豆油5吨，价款也为1.6万元，约定粮油公司于9月1日、10月1日向豆油厂各支付价款1万元和6000元。7月20日，豆油厂向粮油公司供货时，向粮油公司借了800千克面粉，约定10月20日归还。同年8月中旬，粮油公司向豆油厂送货时，向豆油厂借了1吨豆饼，约定于同年9月1日归还。1999午9月1日，豆油厂函告粮油公司，表示愿意以其大豆款1.6万元与粮油公司的豆油款1.6万元相抵；其所借的800千克面粉与粮油公司欠其的1吨豆饼相抵。粮油公司不同意，表示在1999年9月1日只能抵销1万元，剩余6000元必须按合同规定支付；而其所应支付的剩余豆油款也将于10月1日归还。至于面粉与豆饼，粮油公司不同意抵销。双方发生争执，粮油公司诉至法院，请求法院判决豆油厂支付大豆款6000元，归还面粉800千克。 双方的债权债务可否抵销为什么
设char s[3]="AB"，*p=s；，则*(p+2)的值是______。
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