单项选择题

In the past people did not question the difference between life and death. They could 1 that a person died when his heart stopped beating. They learned, however, that the body did not die 2 hen the heart stopped beating. They also discovered that humans remained alive 3 their brain remained active.
Today the difference between life and death is not as easy to see 4 in the past. Modern medical devices can 5 the heart beating and the lungs breathing long 6 the brain stops. But is this 7
The question has caused much debate 8 doctors in the United States. Many of them want a law that 9 a person is dead when the brain dies. A person would then be 10 dead when brain waves stop, even if machines can keep the body alive.