In this step, you will add a C1ComboBoxExtender control to associate with the DropDownList to create the combobox.
<cc1:C1ComboBoxExtender ID="C1ComboBoxExtender1" runat="server" TargetControlID="DropDownList1">
</cc1:C1ComboBoxExtender>
Now you can begin setting properties for the C1ComboBoxExtender to format the DropDownList.