Ana čita knjiguAna is reading a bookIn the accusative case, the words that the action is done to have their endings changed, in this instance, the book is being read, so to mark that this action is being done to the book, it changes from knjiga to kniguNoteIn the accusative case, the words that the action is done to have their endings changed, in this instance, the book is being read, so to mark that this action is being done to the book, it changes from knjiga to knigu