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问题 选择题

为证明细菌对植物遗体的分解作用，某同学做了下面4个实验，在每个实验前，都将数量相同、形状大小基本相同的同种树的落叶分成甲、乙两组。（实验过程中滴加无菌蒸馏水，使树叶保持潮湿。）你认为哪一个实验更能证明细菌对植物遗体的分解作用                      

A．甲组直接放在无菌条件下，乙组直接放在自然条件下

B．甲组灭菌后放在无菌条件下，乙组直接放在自然条件下

C．甲组灭菌后放在无菌条件下，乙组灭菌后放在自然条件下

D．甲组灭菌后放在无菌条件下，乙组灭菌后接种细菌，再放在无菌条件下

答案

答案：D

要设计对照实验，先将两组都进行灭菌处理，排除一些其他因素的干扰，提高实验的准确性。

选择题

受精的鸡卵的结构特点是（　　）

A．胚盘的颜色浓而且大

B．胚盘的颜色浓而且小

C．胚盘的颜色淡而且大

D．胚盘的颜色淡而且小
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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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