9. have eaten --> ate

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

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

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13. Have you / been to

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14. Ted is going to book

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17. b, c, d

a : rose --> rises

e : didn't --> hasn't

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18. d

a : was knowing --> knew

d : getting --> get

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19. d

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20. Are you going to go to the party?