I found this questions asking how to do this in many different forums, so I will describe here how to implement a solution using PHP and AJAX.
The logical flow for the problem should be:
Write an event handler for the first drop down box to get …
The viewer will learn the basics of jQuery, including how to invoke it on a web page.
Reference your jQuery libraries: (CODE)
Include your new external js/jQuery file: (CODE)
Write your first lines of code to setup your site for jQuery.: (CODE)