Saber si un dropdownlist ha sido modificado

[programadorvip]

hola tengo el siguiente codigo donde recorro todos mis dropdownlist alguien podria decirme como decirle si ya esta seleccioando

Código:

Try
            If Page.IsPostBack Then
                '       sqldemostracion.InsertCommand = "insert into encuesta(" & Cbo1.SelectedValue & ";" & 1 & ""

                Dim a As Object = ""
                For Each a In DIV1.Controls
                    If TypeOf a Is DropDownList Then
                        ' If a¿? = ¿? Then

                            Label1.Text = "Seleccione sus 3 cursos"
                            Exit Sub

                        End If
                    End If
                Next



                Dim cn As New SqlConnection(sqldemostracion.ConnectionString)
                Dim sql As String = "insert into encuesta(Id_curso,nivel) values(" & Cbo1.SelectedValue & "," & 1 & ")"
                ' Response.Write(sql)
                Dim cmd As New SqlCommand(sql, cn)
                cn.Open()
                cmd.CommandType = Data.CommandType.Text
                cmd.ExecuteNonQuery()
                sql = "insert into encuesta(Id_curso,nivel) values(" & Cbo2.SelectedValue & "," & 2 & ")"
                cmd.CommandText = sql
                cmd.ExecuteNonQuery()
                sql = "insert into encuesta(Id_curso,nivel) values(" & Cbo3.SelectedValue & "," & 3 & ")"
                cmd.CommandText = sql
                cmd.ExecuteNonQuery()
                cn.Close()
                Button1.Enabled = False
                Response.Write("<script language=javascript>  function cerrar()   {   window.close();   }")
            End If
        Catch ex As Exception
            Response.Write(ex.Message)
        End Try