Exercise 1
1. D 2. B 3. A 4. A 5. B 6. A 7. A 8. D 9. C 10. C
Exercise 2
1. D (改为:have been knocked )
2. B (改为:have gone)
3.D (改为:have)
4. C (改为:could)
5. B (改为:review this chapter)