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问题 单项选择题

有一截面均匀的封闭圆筒，中间被一光滑的活塞分隔成两边，如果其中的一边装有0.1kg某一温度的氢气，为了使活塞停留在圆筒的正中央，则另一边应装入同一温度的氧气质量为（）。

A.3.2kg

B.1.6kg

C.0.8kg

D.

答案

参考答案：B

解析：

当活塞停在圆筒中央时，活塞两端所受的压强相等，即氢气的压强ph和氧气的压强P。相等，ph＝p0，

由理想气体状态方程

得氢气的压强为

式中Mh为氢气的摩尔质量，mh为氢气的质量。

氧气的压强为

式中Mo为氧气的摩尔质量，mo为氧气的质量。

所以

故选择答案B。

[点评] 本题使用理想气体状态方程并结合题目中提供的已知量找到在一定条件下，不同的气体质量与压强的关系，并利用压强P相同，便可解出本题。

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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问答题 简答题

可编程控制器的主要元件有哪些？
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