1. A letter was being written by him. 2. The room had been cleaned by us. 3. He is known to me. 4. The homework has been done by me. 5. The exercise had been done by me.
Hope this helps! Remember that you are using passive voice when the subject is being acted upon by the verb.
national geographic Is a good website to use and wikipedia but I think that will be more confusing cause of the small words they use and half of it I dont understand it
