关于事件的响应问题

Question

Private Sub ImageButton4_Click(ByVal sender As System.Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles Imagebutton4.Click, Imagebutton5.Click, Imagebutton7.Click
        If sender Is Imagebutton4 Then
            Response.Write("<script language='javascript'>window.open('votechart.aspx?type=attitude','Beginpage','width=680,height=380')</script>")
        ElseIf sender Is Imagebutton5 Then
            Response.Write("<script language='javascript'>window.open('votechart.aspx?type=efficiency','Beginpage','width=680,height=380')</script>")
        Else
            Response.Write("<script language='javascript'>window.open('votechart.aspx?type=loss','Beginpage','width=680,height=380')</script>")
        End If
      
    End Sub