Passage Four
Scientists have devised a way to determine roughly where a person has lived using a strand of hair, a technique that could help track the movements of criminal suspects or unidentified murder victims.
The method relies on measuring how chemical variations in drinking water show up in people‟s hair.
“You‟re what you eat and drink, and that‟s recorded in your hair,” said Thure Cerling, a geologist at the University of Utah.
While U.S diet is relatively identical, water supplies vary. The differences result from weather patterns. The chemical composition of rainfall changes slightly as rain clouds move.
Most hydrogen and oxygen atoms in water are stable, but traces of both elements are also present as heavier isotopes（同位素） . The heaviest rain falls first. As a result,storms that form over the Pacific deliver heavier water to California than to Utah.
Similar patterns exist throughout the U.S. By measuring the proportion of heavier hydrogen and oxygen isotopes along a strand of hair， scientists can construct ageographic timeline. Each inch of hair corresponds to about two months.
Cerling‟s team collected tap water samples from 600 cities and constructed a map of the regional differences. They checked the accuracy of the map by testing 200 hair samples collected from 65 barber shops. They were able to accurately place the hair samples in broad regions roughly corresponding to the movement of rain systems.
“It‟s not good for pinpointing,” Cerling said. “It‟s good for eliminating many possibilities.”
Todd Park, a local detective, said the method has helped him learn more about an unidentified woman whose skeleton was found near Great Salt Lake. The woman was 5 feet tall. Police recovered 26 bones, a T-shirt and several strands of hair. When Park heard about the research, he gave the hair samples to the researchers. Chemical testing showed that over the two years before her death, she moved about every two months.
She stayed in the Northwest, although the test could not be more specific than somewhere between eastern Oregon and western Wyoming.
“It‟s still a substantial area,” Park said “But it narrows it way down for me.”
What is the scientists‟ new discovery?
根据题干中“the scientists‟ new discovery”定位到原文第一段第一句“Scientists have devised a way to determine roughly where a person has lived using a strand of hair, a technique that could help track the movements of criminal suspects or unidentified murder victims.”即“科学家已经找到一种办法， 用一缕头发大体判断出一个人生活的地方， 这种技术能够追踪出犯罪嫌疑人或身份不明的受害者的活动情况。 ”故B项符合题意。
What does the author mean by “You‟re what you eat and drink” (Line 1, Para.3)?
根据题干定位到原文第三段“You are what you eat and drink, and that‟s recorded in your hair...”， c项（食物和水会在人体组织中留下痕迹） 最接近文章中的意思， 故选C。
What is said about the rainfall in America‟s West?
文章第五段第一句提到“As a result, storms that form over the Pacific deliver heavier Water to California than to Utah.”即“在太平洋上形成的风暴给加利福尼亚州带来的雨水要比犹他州的比重更大一些。”加州属环海地区， 犹他是内陆地区，B项The water it delivers becomes lighter when it moves inland（雨水由沿海进入内陆地区时比重会变小） 是对原文的概括， 最贴近文意， 故选B。
What did Cerling‟ team produce in their research?
根据题干中“Cerling‟s team”定位到原文第七段第一句“Cerling‟s team collected tap water samples from 600 cities and constructed a map of the regional differences.”团队从600个城市收集了自来水样本， 并且绘制出一张地区差异图。 题干中问的是Cerling团队的研究成果之一， 选项A（一副显示不同地区自米水差异的地图） 最符合题意， 故选A。
What is the practical value of Cerling‟s research?
根据题干中的“practical value”定位到原文第九段， “It‟s not good for pinpointing, Cerling said. It‟s good for eliminating many possibilities.”该团队研究成果的现实意义就是， 能够缩小众多的可能性。 而根据下文的举例可以看到在犯罪侦察中的实践应用， 即帮助警察缩小侦察范围。 选项C与文章内容完全吻合， 故为正确答案。