ASP.NET

HI All,
Please Explain me , if we select dropdownlist automatically get second dropdownlistDetails and if we select second dropdown list automatically get third dropdownlist details. my dropdownlist control present in gridview(EditItemTemplate field) like this...

<Columns>

 <asp:TemplateField HeaderText="CID">

                <ItemTemplate>

                    <%#Eval("CID")%>

                </ItemTemplate>

                <EditItemTemplate>

                    <asp:DropDownList ID="catep" runat="server">

                    </asp:DropDownList>

                </EditItemTemplate>

            </asp:TemplateField>

            <asp:TemplateField HeaderText="CatId">

                <ItemTemplate>

                    <%# Eval("CatId")%>

                </ItemTemplate>

                <EditItemTemplate>

                    <asp:DropDownList ID="cat" runat="server">

                    </asp:DropDownList>

                </EditItemTemplate>

            </asp:TemplateField>

            <asp:TemplateField HeaderText="CateSubId">

                <ItemTemplate>

                    <%# Eval("CategorySubId")%>

                </ItemTemplate>

                <EditItemTemplate>

                    <asp:DropDownList ID="subcat" runat="server">

                    </asp:DropDownList>

                </EditItemTemplate>

            </asp:TemplateField>

</Columns>