9. have eaten --> ate

yesterday 라는 과거 부사가 있으므로 과거부터 현재까지의 연속적인 개념의 표현인 현재완료 불가하고, 과거시제가 되어야 함.

10. has played the cello since he was nine years old

13. Have you / been to

14. Ted is going to book

17. b, c, d

a : rose --> rises

e : didn't --> hasn't

18. d

a : was knowing --> knew

d : getting --> get

19. d

20. Are you going to go to the party?