1. They had been preparing the medicine for 45 minutes before everything was ready. 2. Doctor had written out the recipes five minutes before I came. 3. We had been looking for a drugstore for about 20 minutes before we found it. 4. I had been reading the medical encyclopedia for a few minutes before I found the desired information. 5. My son had not been waiting even for fifteen minutes when the doctor came. 6. Doctors had worked on this issue for three years before they went on a world scientific conference.