Writing a code to enable/disable each list item in a button list control

 Let's say there's a dropdown list control where you can select your travel destination from New York, San Fransisco, and Tokyo.
There's also a button list control where you can choose your transportation method from plane, train, and bus.
<asp:DropDownList id="dd_destination" runat="server">
     <asp:ListItem>New York</asp:ListItem>
     <asp:ListItem>San Fransisco</asp:ListItem>
      <asp:ListItem>Tokyo</asp:ListItem>
</asp:DropDownList>
                       <asp:RadioButtonList ID="rb_method" runat="server">
                        <asp: ...