A simple declaration for DropDownList can be done as below.

<asp:DropDownList ID="DropDownList1" runat="server"> </asp:DropDownList> 

  If we want to add some items statically it can be added inside the Page as follows.

<asp:DropDownList ID="DropDownList1" runat="server"> <asp:ListItem>Select</asp:ListItem> <asp:ListItem>1</asp:ListItem>       <asp:ListItem>2</asp:ListItem>       <asp:ListItem>3</asp:ListItem> </asp:DropDownList>