how choose one ModalPopupExtender out of two on btnAdd click event?

Question

I have two ModalPopupExtender on btnAdd click event i want to activate one or them on specific condition how can i do it.

   <cc1:ModalPopupExtender ID="ModalPopupExtender1" runat="server"
    cancelcontrolid="Div2" okcontrolid="btnOkay"
    targetcontrolid="btnAdd" popupcontrolid="Panel1"
    popupdraghandlecontrolid="PopupHeader" drag="true"
    >
    </cc1:ModalPopupExtender>
    
    <asp:panel id="Panel1" style="display: none" runat="server" >
            <div class="popup_Container" style="size:auto">
            
                <div class="popup_Titlebar" id="Div1">
                    <div class="TitlebarLeft">Popup Header</div>
                    <div id="Div2"class="TitlebarRight"  ></div>
                </div>

                <iframe id="frameeditexpanse" frameborder="0" src="StoreDataFrom/frmStudentProspects.aspx"
                    scrolling="auto" style="width:550px; height:500px;"></iframe>
                    
                   
                   
            </div>
             <input id="btnOkay" type="button" value="Done" />
                    <input id="btnCancel" type="button" value="Cancel" />
    </asp:panel>
    
    
    <cc1:ModalPopupExtender ID="ModalPopupExtender2" runat="server"
    cancelcontrolid="Div4" okcontrolid="btnOkay"
    targetcontrolid="btnAdd" popupcontrolid="Panel2"
    popupdraghandlecontrolid="PopupHeader" drag="true"
    >
    </cc1:ModalPopupExtender>
    
    <asp:panel id="Panel2" style="display: none" runat="server" >
            <div class="popup_Container" style="size:auto">
            
                <div class="popup_Titlebar" id="Div3">
                    <div class="TitlebarLeft">Popup Header</div>
                    <div id="Div4"class="TitlebarRight"  ></div>
                </div>

                <iframe id="Iframe1" frameborder="0" src="StoreDataFrom/frmCategory.aspx"
                    scrolling="auto" style="width:350px; height:105px;"></iframe>
                    
                   
                   
            </div>
             <input id="Button1" type="button" value="Done" />
                    <input id="Button2" type="button" value="Cancel" />
    </asp:panel>