阅读理解 Dr．Hausman is a hair detective．Once a mountain lion killed a thirteen-year-old boy．The town offered a reward of thousand dollars for anyone who would kill the lion． One day an excited hunter came to the town to say that he had killed the mountain lion．As proof that he had killed the right animal, he showed a ball of human hair．He said he had taken the hair from the stomach of the mountain lion． However, another hunter soon showed up to claim(索要)the reward．He too had a ball of human hair that he said he had taken from the dead lion’s stomach．The town did not know which man to pay．Maybe neither one had killed the right mountain lion．To settle the argument, they decided to turn the whole thing over to Dr．Hausman． Dr．Hausman studied the hair and reported that the second hunter should be paid．The hair in the stomach of the mountain lion he had killed matched the hair of the boy．The whole town was relieved to know for sure that the killer had been found． There are other kinds of detectives who do not wear a uniform, like Hausman, but solve endless mysteries every year．There is, for example, the dust detective．Tiny bits of dust stick to your clothes, your fingernails, your hair, or your shoes．They catch in your nose and in your ears．They tell where you have been and what you have done lately．The dust detective often helps catch a criminal by proving that he has been on the scene of the crime(罪案)． Then there is the wood detective．By studying a piece of wood he can tell what kind of tree the piece of wood came from．He can tell where it was grown, and how old it is．He can even tell you what the weather was like at a certain place the year Columbus landed in America．The growth rings on a tree tell him． | 
