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  3. 共用题干 第二篇CaffeineCaffeine is probably the most widely used drug in the world....

共用题干 第二篇CaffeineCaffeine is probably the most widely used drug in the world....

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问题 共用题干
第二篇

Caffeine

Caffeine is probably the most widely used drug in the world.Humans have been consuming caffeine for
hundreds of years,primarily in the form of coffee,tea,and cocoa. Habitual coffee and tea drinkers had long
been observed to have a lower incidence of non-melanoma（黑色素瘤）skin cancers , although no one knew
why.A recent study found that caffeine affects skin cells damaged by ultraviolet radiation,a main cause of
skin cancer. Caffeine interferes with a protein that cancerous cells need to survive,leaving the damaged cells
to die before they become cancerous. Drinking caffeinated coffee has also been associated with a decreased
incidence of endometrial（子宫内膜的）cancer-that is , cancer of the cells lining the uterus. The strongest
effect appears to be in overweight women,who are at greatest risk for the disease.Researchers believe blood
sugar,fat cells,and estrogen（雌性激素）may play a role. Although the mechanism remains unknown,peo-
pie who drink more than two cups of coffee or tea a day reportedly have about half the risk of developing
chronic liver disease as those who drink less than one cup of coffee daily;caffeinated coffee has also been as-
sociated with lowered risk of cirrhosis（肝硬化）and liver cancer.
While many of caffeine's undesirable effects,such as elevated heart rate and blood pressure,are brief,
some short-term benefits,including pain relief,increased alertness,and increased physical endurance,have
also been attributed to caffeine.As a component of numerous over-the-counter diet pills and pain relievers,
caffeine increases their effectiveness and helps the body absorb them more quickly. By constricting（收缩）
blood vessels in the brain , it can alleviate headaches一even migraines（偏头痛）一and can help counter the
drowsiness（眩晕）caused by antihistamines（抗组胺药）.
Caffeine does not alter the need for sleep,but it does offer a temporary solution to fatigue for people who
need to stay alert. Research has shown that sleep-deprived individuals who consumed caffeine had improved
memory and reasoning abilities,at least in the short term. Studies of runners and cyclists have shown that
caffeine can improve their stamina一hence its addition to energy-boosting sports drinks.
People who consume a lot of caffeine regularly may develop temporary withdrawal symptoms,headache
being the most common,if they quit or cut back on it abruptly. Fortunately,these symptoms last only a day
or two in most cases.Individuals who are more sensitive to the stimulatory side effects of caffeine may want to
avoid it,but most doctors agree that the equivalent of three cups of coffee a day does not harm healthy
people.There is no medical basis to give up daily caffeine and many reasons to include a moderate amount in
one's diet.
选项 Some athletes use caffeine to_________.
A:improve their speed
B:increase their endurance
C:maintain their alertness
D:relax their muscles
答案B
解析由文章第一段第三句中“Habitual coffee and tea drinkers had long been observed to have a lower incidence of non-melanoma skin cancers”可知，有喝咖啡和茶叶习惯的人患黑色素瘤皮肤 癌的可能性较低，故选B。
由文章第二段最后一句中“it can alleviate headaches”可知，咖啡因可以用来治头痛。
由文章第三段最后一句可知，咖啡因能增强跑步运动员和自行车运动员的耐力，即en- durance，故选B。
由文章最后一段前两句话可知，退瘾症状仅持续一到两天，即short-lived，故选D。
由文章最后一段的倒数第二句中“most doctors agree that the equivalent of three cups of coffee。day does not harm healthy people”可知，多数医生都认为一天喝三杯咖啡对健康的人不会产生不良影响，因此可能不会产生什么问题，故选C。
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