Форма общие или специальные вопросы с вопросительным словом дано: we have been friends since childhood, (since when) 2. the rain hasn't stopped yet. (general) 3. the film has been on for a week, (for how long) 4. he had recovered by the time i returned from my leave, (general) 5. he will have worked as a teacher for 20 years by next september, (for how long) 6. the students will have started the discussion by the time you come, (who)