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Here are the completed sentences: 1. I have been a teacher **since** I was 20. 2. Bob has worked in that import-export company **for** ten years. 3. Mits Thomas has taught at my school **since** 1975. 4. I have studied English **since** summer. 5. Jenny has eaten five hamburgers **since** 9 o'clock. 6. The cat hasn't eaten anything **since** yesterday. 7. My parents have been married **for** five months. 8. I have known my best friend **since** Sunday. 9. Kim and Joey have been friends **for** three years. 10. They have traveled in the USA **since** they had money. 11. He's written to her every day **since** she left. 12. John's parents have been living in Germany **for** a long time. 13. She hasn't had a day off **for** five days. 14. I've lost so much flexibility **since** I broke my arm. 15. They have all improved in attitude **since** their mother talked to them. Note: **since** is used for a specific point in time, while **for** is used for a period of time. Here are the correct forms of the verbs: 1. He sometimes comes to see his parents. 2. When I was ten, this road was very narrow. 3. Right now I am attending class. Yesterday at this time I attended class. 4. She could swim at the age of 7. 5. We will live in a comfortable apartment on the Moon in the future. 6. Don't watch this movie. It's terrible! 7. You can't see Tom now, he is having a bath. 8. He usually drinks coffee but today he is drinking tea. 9. - What does she do in the evenings? - She usually plays cards or watches TV. 10. - How long have you lived here? I have lived here since 1970. Here are the correct answers: 1. D. were watching 2. C. have had 3. A. find 4. A. will pollute 5. A. has lived 6. C. went 7. C. has left 8. A. were working 9. B. hasn't made 10. D. has been crying 11. A. was dancing 12. B. Have you seen 13. C. played 14. A. has played 15. C. am working 16. B. They started painting the house four hours ago. 17. B. Lisa hasn't called her sister for three months. 18. C. I last saw my best friend five years ago. 19. C. We have never climbed such a tall mountain before.