Replace the infinitives by the Past Indefinite, the Present Perfect or the Present Perfect Continuous.

1.At last you (to open) the door. I (to ring) for an hour at least, I think. 2. Here you are at last. I (to wait) for you for ten minutes. 3. The workers (to work) hard since Tuesday. 4. The scientists (to carry out) a lot of experiments before they (to get) positive results. 5. It (not to rain) for a long time. 6. He (to work) at this project for a long time and(not to finish) it yet. 7. How long you (to know) her? I (to know) her for three years. 8. Last night my friends and I (to decide) to stay in town for I lie summer. 9. They (to discover) diamonds in South Africa in the 19th century. 10. The concept of the atom (not to exist) before 1804.

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2013-03-04T14:40:27+04:00

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1.At last you  have opened the door. I have been  ringing  for an hour at least, I think. 2. Here you are at last. I have been  waiting  for you for ten minutes. 3. The workers have been  working  hard since Tuesday. 4. The scientists have carried out a lot of experiments before they get positive results. 5. It  has been  raining  for a long time. 6. He has been  working at this project for a long time and has not finished it yet. 7. How long have you been   knowing her? I have been knowing her for three years. 8. Last night my friends and I  decided to stay in town for I lie summer. 9. They  discovered diamonds in South Africa in the 19th century. 10. The concept of the atom has not to existed before 1804.