<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<html>
<head>
<title>Seleção</title>
</head>
<h2>Cidades</h2>
<form>
<select name="cidades" >
<option>
<option>Londres
<option>Paris
<option>Roma
<option>Madri
</select>
</form>
</html>
