Reading Why did J.K. Rowling write the Potter books? What was her life like before the first book was published? Was she immediately successful with her first story? Have the book been more successful in the U.S. or U.K.? How old was she when the first book? Has she profited from all of her books?
The subject of the action is unknown Its uses
The subject of the action is unimportant
We want to focus on new information by putting it at the end of the sentence
We want to avoid naming or blaming the subject of the action.
Look in your book. Page 63 http://www.ego4u.com/en/cram-up/grammar/passive Types of tenses