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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 peopled 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 US 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. 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 US. By measuring the proportion of heavier hydrogen and oxygen isotopes along a strand of hair, scientists can construct a geographic 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?
文章第一段提到了“ Scientists have devised a way to determine roughly where a person has lived using a strand of hair”科学家已经发明了一种方式，通过使用人们的头发来大概决定一个人的居住地。故选B。
What does the author mean by“You're what you eat and drink”（Para. 1)?
根据文章第二段提到的 “While US diet is relatively identical， water supplies vary...Most hydrogen and oxygen atoms in water are stable， but traces of both elements are also present as heavier isotopes”可矢口美国的饮食都是 相似的。但是引用的水却是有很大不同。水中的氢和氧是稳定的，但是两者成分在同位素中是有迹可寻的。 故可知人类的饮食会在人体组织中留下痕迹。故选C。
What is said about the rainfall in America's West?
根据文章第二段提到的“The heaviest rain falls first. As a result， storms that form over the Pacific deliver heavier water to California than to Utah”，可知来自太平洋的暴雨在加利福尼亚会比在犹太州的大。所以， 越往内陆，雨水会越少。故选 B。
What did Cerling's team produce in their research?
定位到文章第三段“Cerling's team collected tap water samples from 600 cities and constructed a map of the regional differences...roughly corresponding to the movement of rain systems”，由此可知 Ceding 的团队通过研 究不同地区人们的饮用水及其头发中的水成分，来判断降水的移动。故选D 。
What is the practical value of Cerling's research?
根据文章第三段“‘It's not good for pinpointing，’Cerling said. ‘It's good for eliminating many possibilities.’”， 可知此研究的实用价值在于在侦探过程中帮助排出很多可能性。故选C。