How do detect previous checked radio button in ASP.NET

[hy]

Hi all,
I got the question about the radio button. How do i
detect previous checked radio button after i checked
other's radio button.
While the new radio button checked, it need to prompt out
a confirm message box, if user click on the 'cancel'
button, system will programatically check the previous
radio button instead of the latest radio button that
checked.


Thanks a lot.