How can I refresh a dropdownlist during an event of another dropdownlist without refreshing whole web page?

Question

I am developing my first asp.net website, my requirement is to refresh DropDownListB at SelectedIndexChanged event of DropDownListA, I have set AutoPostBack="True" for DropDownListA. Now the problem is whole web page gets refreshed, its unnecessary for me, is there any other technique that i can use to refresh only that control or only that panel rather than refreshing whole page?

Answer 1

Put the dropdowns inside

 <asp:UpdatePanel ID="up1" runat="server">
                        <ContentTemplate>
// Dropdowns
</ContentTemplate> 
      </asp:UpdatePanel>

and include <asp:ScriptManager ID="sm" runat="server"></asp:ScriptManager> at the top