Lack of Sleep Increases the Risk of Catching a Cold
As cold season approaches, many Americans stock up on their vitamin C and Echinacea(紫锥 花精油). But following the age -old advice about catching up on sleep might be more important. Studies have demonstrated that poor sleep and susceptibility (易受影响) to colds go hand in hand, and scientists think it could be a reflection of the role sleep plays in maintaining the body's defenses. In a recent study for the Archives of Internal Medicine, scientists followed 153 men and women for two weeks, keeping track of their quality and duration of sleep. Then, during a five - day period, they quarantined(进行检疫隔离) the subjects and exposed them to cold viruses. Those who slept an average of fewer than seven hours a night, it turned out, were three times as likely to get sick as those who averaged at least eight hours. Sleep and immunity, it seems, are tightly linked. Studies have found that mammals that require the most sleep also produce greater levels of disease -fighting white blood cells—but not red blood cells, even though both are produced in bone marrow(骨髓) and stem from the same precursor(前体物). And researchers at the Max Planck Institute for Evolutionary Anthropology have shown that species that sleep more have greater resistance against pathogens (病原体). "Species that have evolved longer sleep durations, "the Planck scientists wrote, "appear to be able to increase investment in their immune systems and be better protected. /
单选题
What do many Americans do in the effort to avoid cold in winter?
【正确答案】
A
【答案解析】由题干关键词Americans和cold定位到第一段第一句：As cold season approaches，many Americans stock up on their vitamin C and Echinacea(随着感冒季节的到来，很多美国人买了很多的V—C和紫锥花精油)，很明显买这些东西是为了应对感冒，因此本题的正确答案为A。此题的关键是理解此句中的cold并不是“寒冷”之意，而是指“感冒”。这一点从后面一句话也能够得到提示。
单选题
What did the scientists do in the study for the Archives of Internal Medicine?
【正确答案】
B
【答案解析】由题干关键词the Archives of Internal Medicine定位到第二段。首先scientists followed 153 men and women for two weeks, keeping track of their quality and duration of sleep(科学家们对153名男性和女性受访者进行追踪，记录下他们睡觉的质量和持续时间)，这与B选项内容相符。A选项和D选项在文中并没有提及；C选项中的different kinds ofviruses与原文第二段第二句不符。
单选题
How long did the experiment last according to passage?
【答案解析】本题要求在理解原文的基础上选出与原文相符的选项。第三段第一句说：Sleep and immunity，it seems，are tightly linked，显然睡眠与免疫系统之间的关系只是看起来好像很紧密，并没有得到证实，因此排除A。第三段第二句说mammals that require the．most sleep，also produce greater levels of disease-fighting white blood cells，很显然不是B和D选项中的red blood cells，因此排除B和D。
单选题
Where is white blood cells produced?
【正确答案】
C
【答案解析】文章第三段第二句指出：both are produced in bone marrow(两者都产生于骨髓)，这里的both指的就是前面的white blood ceils和red blood cells，因此本题的正确答案为C。此题干扰性最强的是D，而文中对precursor的功能的描述是白细胞和红细胞都stem from the same precursor，显然它是合成白细胞和红细胞的成分，因此排除。