American writers often break from literary tradition because, the audience always wants something new, surprising, unusual, etc. Like anything else on this world Authors change. I believe that writers are justified in challenging the status quo because literacy is an art, and like any kind of art it evolves and changes creating new things. Any attempt to stop change is simply wrong and insult against creativity.
Theme is a universal lesson learned and central idea is one sentence main idea.
Because the junk food is yummy and smells so tasty, so they eat it, then they get addicted to the food then they start eating more.
