How much lead is harmful? Until the 1970s, exposure to lead was considered dangerous only at blood levels associated with extreme symptoms of poisoning: convulsions (惊厥), brains swelling, acute kidney disease, stomach pains and hallucinations (幻觉). But low -level lead poisoning can cause symptoms that, while subtle, are no less serious. As a result, the CDC has continually lowered the point at which patients should be treated for lead poisoning. One of the most influential study of lead' s low - level effects was published by Herbert Needleman, professor of psychiatry at the University of Pittsburgh Medical School. Testing first and second grade students in the Boston area, he found the lowest I. Q. , academic achievement, language skills and attention span among children with the highest tooth levels (起损害作用的量) of lead. "None of their lead levels exceed the CDC's 1979 toxicity threshold. "Says Paul Mushak, an expert on toxic substances, "Our children and people in the risk groups shouldn't be held hostage (成为人质) to a preventable disease. " What can be done? In some cases the treatment for low - level lead poisoning can be as simple as removing the source of pollution, for example, to stop drinking tap water in some cases. But no one knows the long - term effects of lead poisoning may be. The small amount of research done so far suggest that intellectual impairment may be irreversible (不可逆的). Nor is it always easy to know what water is safe. Jeanne Briskin, a policy analyst with the EPA, reports that in uncounted schools across the country water in drinking fountains may be lead - contaminated. Even the child whose parents have removed the lead threat at home may still be gulping (吞咽)the metal every school day. The American Academy of Pediatrics recommends that children be screened for lead poisoning at 12 months of age, with their doctor to determine follow - up examinations; men at risk for hypertension (高血压) should also have their blood lead levels tested. Prevention is even more important. Public -health specialists have intensified efforts to control the pollutant. Meanwhile, for the individual, that means testing potential household sources of contamination.
单选题
Before the 1970s, exposure to lead was considered safe unless
【正确答案】
B
【答案解析】根据题干定位到第一段第一句：Until the 1970s, exposure to lead was considered dangerous only at blood levels associated with extreme symptoms of poisoning(直到20世纪70年代，铅接触只有在达到了与许多极端的中毒症状相关的非常严重的程度时才会被认为是危险的)，四个选项中B选项与此相符，故为本题的的正确答案。
单选题
Which of the following statements is true about the study conducted by Herbert Needleman according to the passage?
【正确答案】
C
【答案解析】根据题干定位到第二段：Testing first and second grade students in the Boston area(检测了波士顿地区的一、二年级学生)，由此排除A；he found the lowest I. Q. , academic achievement, language skills and attention span among children with the highest tooth levels of lead(他在体内铅含量达到了最高损害程度水平的孩子中发现，他们的智力水平最低，学习成绩和语言能力最差，注意力集中时间最短)，由此排除了B；"None: of their lead levels exceed the CDC's 1979 toxicity threshold. " Says Paul Mushak(保罗·穆沙克说：“所有这些孩子的体内铅含量都没有超过美国疾病控制中心1979年制定的有毒最低限量)，可见C选项与此相符，故为正确答案；本段第一句就指出这个研究是研究低铅含量影响的，故排除D选项。
单选题
One way to treat low -level lead poisoning is to
【正确答案】
A
【答案解析】根据题干定位到第三段第二句：In some cases the treatment for low-level lead poisoning can be as simple as removing the source of pollution, for example, to stop drinking tap water in some cases(在有些情况下，对于低含量的铅中毒的治疗非常简单，只是消除污染源，例如在某些情况下停止喝自来水)，由此可见A选项与原文相符，故为正确答案。而C选项与上面内容不符，故排除；B选项在文中没有涉及，故排除；根据常识，我们知道合格的食物当中是不含有铅的，因此排除D选项。
单选题
The American Academy of Pediatrics recommends that all the following groups of people should be tested for lead poisoning EXCEPT
【正确答案】
D
【答案解析】根据题干定位到倒数第二段：The American Academy of Pediatrics recommends that children be screened for lead poisoning at 12 months of age, with their doctor to determine follow-up examinations: men at risk for hypertension should also have their blood lead levels tested(美国儿科研究院推荐儿童在12个月时应该进行体内铅含量的检查，后继的检查有他们的医生来决定；有高血压危险的男性也应该进行体内血铅含量的检查)，对照选项与此段内容会发现，只有D选项不在被推荐的行列之内，因此本题的正确答案为D。
单选题
For the individual, prevention means
【正确答案】
B
【答案解析】根据题于定位到最后一段：Prevention is even more important. Public-health specialists have intensified efforts to control the pollutant. Meanwhile, for the individual, that means testing potential household sources of contamination(预防更加重要。公共健康专家加强了控制这一污染物的努力。同时，对于个人来说，这意味着要检测可能的家庭污染源)，显然与此相符的是B选项，因此本题的正确答案为B。