In the past people did not question the difference between life and death

. They could11that a person died when his heart stopped beating. They learned, however, that the body did not die12when the heart stopped beating. They also discovered that humans remained alive13their brain remained active.

Today the difference between life and death is not as easy to see14in the past. Modern medical devices can15the heart beating and the lungs breathing long16the brain stops. But is this17？

The question has caused much debate18doctors in the United States. Many of them want a law that19a person is dead when the brain dies. A person would then be20dead when brain waves stop, even if machines can keep the body alive.

11. a. discover b. doubt c. convince d. see

12. a. immediately b. accidentally c. suddenly d. unexpectedly

13. a. even if b. before long c. long before d. as long as

14. a. as b. like c. such as d. the same

15. a. trace b. keep c. pursue d. increase

16. a. while b. afterward c. after d. before

17. a. alive b. life c. live d. lively

18. a. from b. about c. between d. among

19. a. insists b. claims c. says d. tells

20. a. decided b. considered c. determined d. estimated