[Rails] Masalah dengan prototype.js

Guys..tolongin..

Saya coba manggil sebuah action di view dengan kode spt ini 

<%= collection_select :address, :country_id, @countries, :id, :name,
{:include_blank => true}, {:onchange => 'showProvinces(this.value)'} -%>

saat onchange, function showProvinces (javascript) akan di panggil.
Isi function showProvinces kaya gini 

var url = '/user/find_provinces/' + country_id;
    new Ajax.Request(url, {
      method: 'post',
      onSuccess: function(transport) {
        alert(transport.responseText);
      }
    });

dan action find_provinces saya kaya gini 

def find_provinces
    @provinces =  Province.find(:all, :conditions => [ "country_id =
?", params[:id] ])
    if (request.xhr?)
      render :text => @provinces.to_json    
    end
  end

saya ingin apa yang dikembalikan oleh method find_provinces itu akan
muncul di alert yang saya panggil di view

mohon pencerahannya ya :)

------------------------------------

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