If you are looking at cascading drop down lists, refer to this link to do the required task with the help of simple jquery.
Link
Refer to Arun P Johnny's answer who also provides a Demo.
jQuery(function($) {
var locations = {
'Germany': ['Duesseldorf', 'Leinfelden-Echterdingen', 'Eschborn'],
'Spain': ['Barcelona'],
'Hungary': ['Pecs'],
'USA': ['Downers Grove'],
'Mexico': ['Puebla'],
'South Africa': ['Midrand'],
'China': ['Beijing'],
'Russia': ['St. Petersburg'],
}
var $locations = $('#location');
$('#country').change(function () {
var country = $(this).val(), lcns = locations[country] || [];
var html = $.map(lcns, function(lcn){
return '<option value="' + lcn + '">' + lcn + '</option>'
}).join('');
$locations.html(html)
});
});