Should I include two css file or one is enough?
<link rel="stylesheet" href="bootstrap/css/bootstrap.min.css" media="all" />
<link rel="stylesheet" href="bootstrap/css/bootstrap-responsive.min.css" media="all" />
OR
<link rel="stylesheet" href="bootstrap/css/bootstrap-responsive.min.css" media="all" />
Bootstrap 2
You should include both, the first one defines all the styles for html elements whilst the second one adds responsiveness to the layout.
Bootstrap 3
Only one css file will be included.
Happy coding!