A、A person is dangerous. B、Criminals are lying. C、Criminals are identical. D、A person is innocent. D讲座最后讲到“DNA鉴定可以用来确定一个人是否有罪，许多

As long as there has been crime, there have been ways to solve it. [16] One of the oldest methods is interrogation, a method in which the police question people who might have committed the crime or who might have information about the crime. Interrogation can help the police to establish many basic facts, but modem techniques for solving crime include more complex scientific methods.
    Let me talk first about a system often called "crime hotlines". In some cases, where law enforcement personnel have difficulty finding a criminal, they turn to private citizens for help in solving a crime. [17] 1This system allows people to make a phone call or access a website and give information to the police anonymously. This can often be effective when people are afraid to give information in public. Sometimes, a family member may have committed the crime, and another family member finally decides to call the police and give the information they have.
    Second, fingerprinting. Each person’s finger print is unique. The ancient Chinese used finger prints to sign legal papers. What better way to identify an individual? Yet, it was only in the late 19th century that finger prints were first used to identify criminals. A variety of scientific techniques makes it possible for finger prints to be lifted from most surfaces.
    A relatively new technique that crime-fighters are now using is called "psychological profiling". Criminal psychologists look at the crime and the way it was committed. Based on this information, they try to understand the personality and motivation of the person who committed the crime. Then they can focus their search on people who match this profile.
    In some cases, private citizens are finding ways to solve crimes as well. With a little knowledge of electronics, anyone can put hidden cameras in a home or office. In the 1990s as an example, there were some cases where nannies were accused of abusing the children they were paid to care for. [18] Hidden cameras were used to prove the nanny’s guilt. However, the technique is controversial because it involves issues of privacy.
    Finally, let me discuss DNA. Of the most recent crime-solving techniques used, DNA is proving very effective. Each person, with the exception of identical twins, has a unique DNA coding system. So, if criminals leave anything that can be tested at the scene of the crime, such as blood or hair, they can be identified. DNA was used to solve a crime for the first time in England in 1987. Since that time, it has become widely used, and it’s considered 99% accurate. [19] DNA testing can also be used to prove that a person is innocent. Many prisoners have been released because DNA evidence proves that they did not commit the crime of which they were convicted.
    16. What is the oldest method to identify criminals?
    17. What is the advantage of crime hotlines?
    18. Why is it controversial using hidden cameras in solving a crime?
    19. What can DNA testing prove?