Check (Select) only one of multiple RadioButtons in ASP.Net

dear fellas, 

i have 4 radio buttons and im using this radio buttons as panel extender collapse and extend id. such as :

<cc1:CollapsiblePanelExtender ID="collapsingle" runat="server"  CollapseControlID="rdbtn_single" Collapsed="True" CollapsedSize="0" ExpandControlID="rdbtn_single" TargetControlID="pnl_single"></cc1:CollapsiblePanelExtender>

<cc1:CollapsiblePanelExtender ID="collapmarried" runat="server"  CollapseControlID="rdbtn_married" Collapsed="True" CollapsedSize="0" ExpandControlID="rdbtn_married" TargetControlID="pnl_married"></cc1:CollapsiblePanelExtender>

<asp:RadioButton ID="rdbtn_single" runat="server" Text="Single" ValidationGroup="status" />

<asp:RadioButton ID="rdbtn_married" runat="server" Text="Married" ValidationGroup="status" />

but even i already set their validationgroup. i cant choose only one option only. how i can achieve this?