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问题 选择题

下列关于金属钠的说法中正确的是（　　）

A．钠在空气中易变质，最后变为过氧化钠

B．钠在空气中燃烧生成Na2O

C．钠切开后，横断面变暗属于化学变化；焰色反应属于物理变化

D．钠的还原性很强，与硫酸铜溶液反应会置换出红色的铜

答案

A．钠在空气中与氧气反应生成氧化钠，进而与水反应生成氢氧化钠，最终生成稳定的碳酸钠，故A错误；

B．钠在空气中燃烧生成Na2O2，故B错误；

C．钠切开后，横断面变暗，钠被氧化生成氧化钠，属于化学变化；焰色反应为元素的性质，属于物理变化，故C正确；

D．钠与水剧烈反应，加入到硫酸铜溶液中，生成氢氧化铜和氢气，故D错误．

故选C．

单项选择题

Celebrate. Celebrate. Physicians are delighted with a Food and Drug Administration (FDA) advisory panel’s recommendation earlier this year that Vioxx and its cousins Bextra and Celebrex (all medicines known as Cox-2 inhibitors) should remain on the market, despite evidence they increase heart disease risk in some people. The panelists reached their decision after weighing all the data and concluding the benefits of these pain-relieving drugs outweighed the risks.
Specifically, these scientists acknowledged that, for some patients, these prescription drugs were uniquely effective in reducing pain from arthritis and other causes. For others—concerned about ulcers associated with aspirin and other OTC analgesics—the Cox-2 inhibitors offered the advantage of minimizing potentially serious effects of stomach irritation.
Now is an appropriate time for everyone to take a fresh look at the benefit-risk equation for Vioxx and the other Cox-2 inhibitors.
The risks-increased risk of heart disease in some who use the drugs—have been well publicized. Much less publicity has been given to a spectrum of real and potential benefits that go way beyond reduced risk of stomach irritation. These little-discussed benefits would have been lost, perhaps permanently-had Vioxx, Bextra and Celebrex been driven from shelves in pursuit of perfect safety, an unattainable goal.
For example, there is substantial evidence Cox-2 inhibitors can reduce development of colon polyps, which may become colon canceL Indeed. Celebrex is FDA-approved for those genetically prone to colon cancer. Ironically, the 2004 study that revealed the elevated heart attack risk of Vioxx was primarily designed to further establish the drug’s effectiveness in protecting against colon cancer. And while the results of that interrupted trial have not yet been published, there is good reason to believe they will confirm the protective effects against colon cancer established in research over the last 10 years.
At the time of its withdrawal from the market last fall, studies of Vioxx as well as the other Cox-2 drugs suggest that they had other anti-cancer properties as well, possibly reducing the risk of malignancies of a number of sites, including the lung and esophagus.
Had these drugs been dismissed, their untapped promise for prevention would have evaporated well before it was evaluated and applied to save lives. Fortunately, cooler and wiser heads prevailed.

What does the passage say about Cox-2 inhibitors

A．They could prevent arthritis.

B．Their functions have been exaggerated.

C．They could relieve some stomach problems.

D．Their risks and benefits are identical.
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单项选择题

土地利用年度计划实行（）管理。

A.指导性

B.指令性

C.市场化

D.强化性
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