5 Dependant Drop Downs

I have a question regarding the 3 dependent php drop down. I need 5 dependent drop down menus, where each is dependent on the other. i also need to make it that the user can get redirected from the 4th menu and/or the 5th menu. I need to use PHP because I have over 50,000 redirects that are possible, and do not want to hard code the options into the HTML Page. I'm barely OK at PHP and am learning as much as I can, but I can't seem to connect the 4th and 4th menu's, nor can I get a redirect from any of them. At this point the 3 menu's do work on my site.

My Menu's will need to look like this:

1) --SELECT SPORT--
2) --SELECT MAKE--
3) --SELECT MODEL--
4) --SELECT YEAR-- (OPTIONAL REDIRECT FROM SUBMIT BUTTON)
5) --SELECT CATEGORY-- (REDIRECT FROM SUBMIT BUTTON)

I appreciate any help than is given.