Why do authors use tension in a story

Authors use tension so that it creates for excitement and is more interesting for the reader/audience. By telling the story backwards or by telling the story in bits and pieces to finally join all the pieces and show you a masterpiece( the whole picture). By heightening the emotions of the characters and the situations. An example of dramatic irony is when the author uses Oedipus not knowing he was the killer and making a promise that he shall kill the person who killed his father. 

The correct answer is option a.