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问题 选择题

世界上分布最广的人种是（       ）

A．黄种人

B．黑种人

C．白种人

D．棕色人种

答案

答案：C

题目分析：白种人主要分布在欧洲、北美洲、大洋州、非洲北部和亚洲西部和南部，可见白色人种是世界上分布最广的人种，故选C．

填空题

Five Painful Facts You Need to Know


0. First of all, let’s set the record straight: Pain is normal. About 75 million U.S. residents endure chronic or recurrent pain. So what is pain and why do so many suffer so long Pain is felt when electrical signals are sent from nerve endings to your brain, which in turn can release painkillers called endorphins and generate reactions that range from instant and physical to long-term and emotional. Beyond that, scientific understanding gets painfully fuzzy. Here’s what’s known:
1. When you’re in pain, you know it. But if scientists could fully grasp how pain works and why, they might be able to help you more. The American Academy of Pain Medicine defines pain as "an unpleasant sensation and emotional response to that sensation." Some pain is the result of an obvious injury. Other times, it is caused by damaged nerves that are not so easy to pinpoint. "Pain is complex and defies our ability to establish a clear definition," says Kathryn Weiner, director of the American Academy of Pain Management. "Pain is far more than neural transmission and sensory transduction. Pain is a complex mixture of emotions, culture, experience, spirit and sensation."
2. If you have chronic pain, you know how demoralizing and debilitating it can be, physically and mentally. It can prevent you from doing things and make you irritable for reasons nobody else understands. But that’s only half the story. People with chronic backaches have brains as much as 11 percent smaller than those of non-sufferers, scientists reported in 2004. They don’t know why. "It is possible it’s just the stress of having to live with the condition," said study leader A. Vania Apkarian of Northwestern University. "The neurons become overactive or tired of the activity."
3. It may not eliminate the phrase "Not tonight, honey ..." but a 2006 study found that migraine sufferers had levels of sexual desire 20 percent higher than those suffering from tension headaches. The finding suggests sexual desire and migraines might be influenced by the same brain chemical, and getting a better handle on the link could lead to better treatments, at least for the pain portion of the equation.
4. Any man who has watched a woman having a baby without using drugs would swear that women can tolerate anything. But the truth is, it hurts more than you can imagine. Women have more nerve receptors than men. As an example, women have 34 nerve fibers per square centimeter of facial skin, while men average just 17. And in a 2005 study, women were found to report more pain throughout their lifetimes and, compared to men, they feel pain in more areas of their body and for longer durations.
5. Animal research could offer clues to eventually relieve human suffering. Take the naked mole rat, a hairless and nearly blind subterranean creature. A study this year found it feels neither the pain of acid nor the sting of chili peppers. If researchers can figure out why, they might be on the road to new sorts of painkilling therapies for humans. In 2006, scientists found a pathway for the transmission of chronic pain in rats that they hope will translate into better understanding of human chronic pain. Lobsters feel no pain, even when boiled, scientists said in a 2005 report that is just one more salvo in a long-running debate.
A. Women feel more pain
B. Chronic pain is common
C. Chronic pain shrinks brains
D. Migraines and sex go together
E. Pain brings about more stress
F. Scientists don’t understand pain fully
G. Animal research may relieve human pain

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