问题详情：
You can tell a lot about people by looking at their hair – not just whether they brush, spray or blow-dry. 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. The liquid makes up more than half an adult human’s body weight. Our bodies break water down into hydrogen(*) and oxygen. Atoms of these two elements end up in our tissues, fingernails, and hair.
But not all water is the same. Hydrogen and oxygen atoms can vary in how much they weigh. In the case of hydrogen, for example, there are three types according to their weights. Each type is called a hydrogen isotope（同位素）. And depending on where you live, tap water contains different isotopes.
Can hair record this information? That’s what James R. Ehleringer, an environmental chemist at the University of Utah, wondered. To find it out, he and his colleagues collected hair from hair stylists in 65 cities across the United States. Even though people drink a lot of bottled water these days, the researchers have found that people’s hair has the same isotopes as found in local tap water. That’s probably because people usually cook their food with the local water.
Authorities can now use the information to analyze hair samples from criminals or crime victims and narrow their search for clues. For example, one hair sample used in Ehleringer’s study came from a man who had moved from San Francisco to Salt Lake City. As his hair grew, it reflected his change in location.
28. What do we know about the hydrogen isotopes according to Paragraph 3?
A. They are classified by size. B. Each type of them differs in weight.
C. They can improve the quality of tap water. D. Some of them cannot combine with oxygen.
29. Why is it possible to know where people are from by analyzing their hair?
A. People use the same bottled water.
B. People wash their hair in different ways.
C. People’s hair is affected by the weather of the places they stay.
D. People’ hair indicates the type of water in the places they stay.
30. The last paragraph is mainly to show _______.
A. how to recognize criminals B. how to collect hair samples
C. the usefulness of hair analysis D. the process of Ehleringer’s study
31. Which of the following can be the best title for the passage?
A. Water composition B. Change your hair C. Hair detectives D. No way out
【回答】
BDCC
知识点：科普环保类阅读
题型：阅读理解
