单项选择题

You create a Microsoft ASP.NET application by using the Microsoft .NET Framework version 3.5. You write the following code fragment:  
<asp:ScriptManager ID="ScriptManager1" runat="server" />  
<asp:UpdatePanel ID="updateLabels" runat="server" UpdateMode="Conditional">  
<ContentTemplate>  
<asp:Label ID="Label1" runat="server" />  
<asp:Label ID="Label2" runat="server" />  
<asp:Button ID="btnSubmit" runat="server" Text="Submit"   onclick="btnSubmit_Click" />  </ContentTemplate>  
</asp:UpdatePanel>  
<asp:Label id="Label3" runat="server" />   
You need to ensure that when you click the btnSubmit Button control, each Label control value is asynchronously updatable. 
Which code segment should you use?（）