Cloze Test (10 points, 1 point for each)

下列短文中有十个空格，每个空格有四个选项。根据上下文要求选出最佳答案，并在答题卡上将相应的字目涂黑。

In the past people did not question the difference between life and death. They could 11 that a person died when his heart stopped beating. They learned, however, that the body did not die 12 when the heart stopped beating. They also discovered that humans remained alive 13 their brain remained active.

Today the difference between life and death is not as easy to see 14 in the past. Modern medical devices can 15 the heart beating and the lungs breathing long 16 the brain stops. But is this 17 ?

The question has caused much debate 18 doctors in the United States. Many of them want a law that 19 a person is dead when the brain dies. A person would then be 20 dead when brain waves stop, even if machines can keep the body alive.