单项选择题

A.Add the following marktip to UpdatePanel1.  <Triggers>  <asp:PostBackTrigger ControlID="btnSave" />  </Triggers>  
B.Set the UpdateMode property for the UpdatePanel2 to "Always"
C.Add the following markup to UpdatePanel2  <Triggers>  <asp:AsyncPostBackTrigger ControlID="btnSave"  EventName="Click" />  </Triggers>  
D.Set the UpdateMode property for UpdatePanel2 to "Conditional"