Change the Value of Parent Dropdown using Jquery and the child will show the data

I am just using this article, and i just added a button to change the parent dropdownlist

http://www.aspsnippets.com/Articles/AJAX-Cascading-DropDown-Example-in-ASPNet.aspx

$("#ctl00_contentplaceholder1_ddlCountries").val(2); 
$("#ctl00_contentplaceholder1_ddlStates").val(4);
$("#ctl00_contentplaceholder1_ddlCities").val(7);