C. For telling her to be careful during the trip.
听第10段材料，回答第17至20题。
17. What is a blood transfusion?
A. Losing a lot of blood in a serious accident or a difficult operation.
B. Finding out the amount of blood a patient needs for an operation.
C. Taking blood from someone else and putting it into a patient’s body.
18. What finally made almost every blood transfusion successful?
A. The discovery of blood types.
B. The founding of a blood bank.
C. The experiment with sheep blood.
19. According to the speaker, if you give 10% of your blood, how long does it take your body to replace it?
A. One week. B. Five days. C. One day.
20. What is the main purpose of the speech?
A. To call on people to give blood.
B. To explain what a blood transfusion is.
C. To review the history of the research on blood.
1. B 2. B 3. B 4. C 5. A 6. A 7. C 8. B
9. C 10. A 11. B 12. A 13. B 14. B 15. C 16. C
17. C 18. A 19. C 20. A
