how to show data in dropdownlist from sqlserver in asp.net using c#

I have three dropdownlist the code below
<asp:DropDownList ID="ForumTitleList" runat="server" AutoPostBack="True"> </asp:DropDownList> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <asp:DropDownList ID="ForumSubTitleList" runat="server" AutoPostBack="True" > </asp:DropDownList> &nbsp;&nbsp;&nbsp; <asp:DropDownList ID="ForumSubjectTitleList" runat="server" AutoPostBack="True" > </asp:DropDownList> and the code behind is

using System; using System.Collections.Generic; using System.Linq; using System.Web ...