In American crime movies, policemen search crime scenes for anything that might bel

   In American crime movies, policemen search crime scenes for anything that might belong to a criminal— bits of fingernail , blood or hair— in order to find out who they are. What they hope to find is the key to their identity—their DNA.

DNA is the chemical that contains a person’s genetic makeup. Every person, except for identical twins, has unique DNA information. That is why we can use it to identify someone.

There is no doubt that DNA evidence is becoming a very powerful tool for law enforcement (实施)officers. In the US, all 50 states and the federal government keep DNA databases of some criminals after they have been convicted（宣告有罪）. Whenever a crime happens, the police collect DNA from the crime scene and compare this with samples they already have in the criminal database. If they match any suspect in the database, then they’ve caught their criminal. Even if they don’t, the DNA sample can still be used to determine the person’s sex, height, hair and eye color and other characteristics. This helps police to create a physical profile of the criminal.

Some people feel that the database should be made bigger to contain everyone’s DNA and help to solve many more crimes. This would also avoid mistakes when someone is wrongly convicted of a crime. DNA doesn’t make mistakes.

However, other people are worried that it would violate their privacy. Someone’s DNA can be used to gather information such as the person’s family and ethnic（种族的） background, whether he or she has a gene mutation（突变）or certain genetic diseases, and other personal issues. People are afraid that this information might be used inappropriately. They may fear that employers might read it and treat them differently. People may also be afraid that personal data might get into the hands of insurance firms or loan companies. For example, if they knew from your DNA that you had a genetic risk of a serious disease, they might be able to refuse you life insurance, a loan, or even a job.

Clearly, the use of DNA evidence will continue to help the police solve crimes. However, social and ethical concerns about DNA will also remain a topic of debate.

47. What is the article mainly about?

A. The possibilities opened up by DNA technology     B. The controversy over DNA databases

C. How DNA databases are built                    D. What role DNA plays in solving crimes.

48. Which is TRUE according to the article?

A. DNA evidence has been widely used in criminal law cases.

B.Everyone in the world has their own unique DNA composition.

C. In America, anyone who has been convicted must submit a  DNA sample.

D. America’s DNA database is the biggest national DNA database in the world.

49. Some people suggest building a database containing everyone’s DNA because _____.

A. it would mean fewer people commit crimes.

B. it would make it more convenient for the government to gather information

C. it would help the police identify suspects more efficiently and accurately

D. such a database could be helpful in many more fields besides solving crimes

50. What is the great concern over the DNA database according to the article?

A. Some people might make use of it to make money.

B. It would threaten people’s individual privacy and rights.

C. The DNA stored in the database might be labeled wrongly.

D.The DNA would have a gene mutation and become inaccurate.

 BACB