title: How do I create multiple select option in rails 4
body: <p>I want a form where a field is displayed if the
  user selects a certain option. Like if the user
  selects USA as a country, below it there should
  be option to select a state from the country
  and from the state select city. Same for
  another country. Please, how do I implement
  this? Am out of ideas. Thanks.</p>