I have three serverside control checkboxes (asp.net) in my page and I would like to enforce the user to select at least one before they click submit button. How can this be done. thank you for your help.

 

<asp:CheckBox ID="ckPrime" runat="server" EnableViewState="False" Font-Bold="False" Text="Prime Contractor" />

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<asp:CheckBox ID="ckSub" runat="server" EnableViewState="False" Text="Sub Contractor" />

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<asp:CheckBox ID="ckTruking" runat="server" Text="Trucking / Broker / ITOs" />

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