A、By judging from their behavior. B、By testing the function of the genes. C、By examining the negative influence around them. D、B

A blood test that can predict whether someone may attempt suicide has been developed by scientists in a breakthrough which could prevent hundreds of deaths. (23) American researchers have found that variations in a single gene can be used to predict if someone is likely to take their own life. Researchers found that the gene SKA2 stopped functioning correctly in people at risk of suicide. The SKA2 gene is found in the brain, and is involved in preventing negative thoughts and controlling hotheaded behavior. If there isn’t enough SKA2, or it is altered in some way, the body cannot control the levels of a chemical called Cortisol. Previous research has shown that people who attempt suicide or who take their own lives have large amounts of the special chemical in their systems. (24) A test could allow doctors or psychologists to place patients on "suicide watch" and restrict their access to drugs or equipment which they could use to end their own life. The research was reported in the American Journal of Psychology. "We need to study this in a larger sample but we believe that we might be able to monitor the blood to identify those who are at risk of suicide," says study leader Dr. Zachary Kaminsky, an assistant professor of psychiatry and behavioral sciences. (25) The blood test managed to predict those with the most severe risk of suicide with 90 percent accuracy. They could also spot if someone had already attempted suicide with 96 percent accuracy, simply by looking at the levels of SKA2.
23. How can American scientists tell whether people are more likely to kill themselves or not?
24. How does the test mentioned stop people from committing suicide?
25. What can be learned about the blood test for suicide risk?