Get and Set radiobuttonlist value

I have a form that has an optional section that displays based on a radiobuttonlist choice and a JavaScript function. All that works fine, but if the section is displayed and choices made in the radiobutton lists, but the user changes their mind and chooses to not display the section their radiobutton list choices are retained. I need to check to see if the section is displayed, if not then clear any choices they may have made in the radiobutton lists in the now hidden section. But I also need to keep data entered in the form not in the optional section.
Here is the code in the form:
<asp:radiobuttonlist runat="server" id="radioButtonList_SI">   <asp:ListItem Text="Yes" Value="Yes" onClick="supBlocks('block');" Selected="True" />   <asp:ListItem Text="No" Value="No" onClick="supBlocks('none');" /> </asp:radiobuttonlist> ...