理工类考试辅导：补全短文Hair Detectives
Scientists have found a way to use hair to figure out where a person is from and where that person has been. The finding could help solve crimes， among other useful applications.
Water is central to the new technique. Our bodies break water down into its parts： hydrogen and oxygen. Atoms of these two elements end up in our tissues and hair.
But not all water is the same. Hydrogen and oxygen atoms can vary in how much they weigh. Different forms of a single element are called isotopes. And depending on where you live， tap Water1 contains unique proportions of the heavier and lighter isotopes of hydrogen and oxygen.
Might hair record these watery quirks2? Thats what James R. Ehleringer， an environmental scientist at the University of Utah in Salt Lake City3， wondered.
To find out， he and his colleagues collected hair from barbers and hair stylists in 65 cities in 18 states across the United States. The researchers assumed that the hair they collected came from people who lived in the area.
Even though people drink a lot of bottled water these days， the scientists found that hair overwhelmingly reflected the concentrations4of hydrogen and oxygen isotopes in local tap water. Thats probably because people usually cook their food in the local water. Whats more， most of the other liquids people drink including milk and soft drinks contain large amounts of water that also come from sources within their region.
Scientists already knew how the composition of water varies throughout the country. Ehleringer and colleagues combined that information with their results to predict the composition of hair in people from different regions. One hair sample used in Ehleringers study came from a man who had recently moved from Beijing， China， to Salt Lake City. As his hair grew， it reflected his change in location.
The new technique cant point to exactly where a person is from， because similar types of water appear in different regions that span a broad area. But authorities can now use the information to analyze hair samples from criminals or crime victims and narrow their search for clues.
词汇：
hydrogen n. 氢 overwhelmingly adv. 压倒性
Atom n. 原子 Isotope n. 同位素
span v. 跨越 Quirk n. 古怪举动；怪僻
clue n. 线索 Stylist n. 发型师
注释：
1. tap water： 自来水，管道供水
2. watery quirks： 水的奇特性质。quirk的含义是“an peculiar or unexpected behavioral habit”(古怪的不可预测的行为和事情)。
3. University of Utah in Salt Lake City： (美国)盐湖城的犹他大学
4. concentrations： 浓度；含量
练习：
1. What does the writer say about tap water? Which of the following is NOT correct?
A) Tap water reflects the concentrations of hydrogen and oxygen isotopes in different regions.
B) Tap water is a kind of soft drink in the United States.
C) Tap water contains unique proportions of isotopes of hydrogen and oxygen.
D) Tap water is used to cook food.
2. James R. Ehleringer tried to find out
A) if our bodies break water down into its parts.
B) if it is possible to collect hair samples across the country.
C) if tap water contains unique proportions of isotopes of hydrogen and oxygen.
D) if the composition of hair can indicate exactly where people are from.