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天然水中阳离子组合假想化合物的顺序是：（）优先组合，（）次之，（）最后组合。阴离子的组合顺序是（）优先组合，（）次之，（）最后组合。

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参考答案：Ca2＋；Mg2＋；Na＋；HCO3－；SO42－；Cl－

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A total of 4.6 million digital televisions have been sold, and the sales of HDTV sets have quadrupled since last year. Consumers have bought HDTVs to play their DVDs and to have clearer pictures and wide screens. Only a small percentage of the people who have purchased HDTVs, however, have actually ^hooked their TVs up# to receive high-definition television digital signals. Perhaps television viewers are having trouble keeping up with the changes in technology. Even the manufacturers of HDTVs, like Mitsubishi, Thomson Multimedia, Sony, and Samsung seem to have a tough time learning how to make their sets work with the various digital TV formats because little standardization has been required or implemented in the industry.Some of the HDTVs weigh over 200 lbs., and a variety of retailers offer a delivery service to the buyer’’s home to help install the heavy sets. This is known as a white-glove service and usually comes with an extra fee. After HDTV purchasers get their sets home and hook them up, they will still need to work to get the digital signals to their systems. Most of the industry’’s cable providers do not yet offer high-definition programing, and only about 15% of commercial television stations have switched over to even the lowest improved digital pictures. Worse yet, viewers may need to install antenna before they can even get the digital signals to their new HDTV sets. Another frustration for home-theater seekers is that the current HDTV sets allow owners only to watch high-definition programs, not to record them.

According to the first sentence, the sales of HDTV sets since last year, by the time when this article was written, had reached________.

A．4.6 million

B．9.2 million

C．18.4 million

D．I do not know how many
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2010年4月14日7时49分40秒，青海省玉树藏族自治州玉树县发生7．1级地震，搜救工作中遇到了很多困难。灾区处于高原地区，海拔高，很多救援队员在救援时出现了不同程度的高原反应，搜索犬的搜索效率、效能也受到了不同程度的影响。产生高原反应的其中一个原因就是气压随高度的增加而_______ （选填“增大”或“减小”）。救援时，救援人员能用撬棒撬起一块较大的石头，这是利用了_______原理。

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