How to combind two dropdown list values into one dropdown list?

Hi All,

I refered some websites, they are combinding two dropdown list values into single, but i don't know .Net will support it or not? If any body knows it plz tell me how to achieve it??

EX: Go to Naukri.com and select Functional Area dropdown list there u can see main & sub category names in one dropdown list!!!

 

Thanks,

Aswath.
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