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从下列事实所得出的相应结论正确的是(  )

序号实验事实结论
①Cl2的水溶液可以导电Cl2是电解质
②将燃烧的镁条放入CO2中能继续燃烧还原性：Mg>C
③常温下白磷可自燃而氮气须在放电时才与氧气反应非金属性：P>N
④某无色溶液中加入氢氧化钠溶液并加热，产生的气体能使湿润的红色石蕊试纸变蓝该溶液中一定有NH4+
 

A.①②      B．②④      C．①③      D．③④

答案

答案：B

氯水导电是因为氯气与水反应的产物盐酸及次氯酸是电解质，氯气不是电解质，①错；镁与CO2的反应中镁是还原剂，C是还原产物，②正确；P在常温下即与氧气反应，而N2要在放电情况下才能与氧气反应，是因为N2分子中的叁键键能特别大使得反应的活化能很大，而且元素的非金属性取决于其得电子能力，在上述两个反应中N和P均表现为还原性而非氧化性，③错；中学范围内能使湿润的红色石蕊试纸变蓝色的气体一定是氨气，而某溶液能与氢氧化钠溶液共热产生氨气则可说明溶液中含有铵根离子，④正确。

填空题

轧账是营业中的重要环节，分为_____轧账和日终轧账。
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问答题

On Feb. 17, 2009, it could snow all across America. Not outside, but in living rooms, on TV sets. That’s the date when broadcasters will switch to digital transmission, rendering millions of standard analog TVs useless. Consumers can avoid this whiteout, but only if they’re prepared. And there’s the challenge: How to inform the roughly 20 million households relying exclusively on analog sets that pull in their reception for free, through rabbit ears or a rooftop antenna. Analog TVs that receive cable or satellite will not be affected.
Consumers who own these sets don’t necessarily need to know why the federal government is mandating the change (to free up the airwaves for other purposes, such as wireless and public safety communications-though added benefits are better pictures and more channels). But they do need consistent and unbiased information on what to do and they need to be able to act on it. With fewer than 18 months to go, though, 56 percent of viewers with analog sets have never even heard of the switch. The General Accountability Office, the government watchdog, is concerned that with two government agencies involved, "no one is in charge."
The Federal Communications Commission is worried, too. "If we don’t do a better job of planning, we’ll have one of the biggest outrages Congress has ever seen," FCC commissioner Jonathan Adelstein told US senators last month. The options for consumers are fairly straightforward. Starting with the least expensive one, they are:

  • a) buying a converter box using government coupons’
  • b) subscribing to cable or satellite TV services, which will make the transition on their end, or
  • c) buying a digital TV. But sharing this information is anything but simple. Because it has only $ 5 million to get the message out, the government is turning to the private sector for help with public-service announcements and educating consumers in stores. This partnership makes sense, if done right. Certainly, the broadcasting industry wants viewers to keep on watching, However, there’s a danger in their self-interest. Naturally, retailers also want people to buy new digital televisions instead of opting for low-cost converters, and cable and satellite providers want new subscribers. And industry may not have enough of a financial incentive to reach out to certain analog viewing groups, such as the poor or elderly (seniors make up 40 percent of analog households).
    Other serious issues remain. One is whether the converter boxes will be uniformly available in stores. Beginning in January, households should be able to apply to the Commerce Department’s National Telecommunications and Information Administration for up to two $ 40 coupons to offset the costs of converter boxes expected to be priced from $ 50 to $70. But some retailers may not stock the boxes if they don’t have much demand for them.
    And what about recycling analog televisions, of which there are an estimated 70 million More than anything, what’s needed is oversight and coordination of the conversion. Congress should designate one of the two government agencies involved in this project to take the lead, or empower an independent group to oversee the transition.


Explain the statement "However, there’s a danger in their self-interest. " (para. 3)
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