using (var connection_ = new FbConnection(connectionString))
{
  var ds = new DataSet();                    
  var adapter = new FbDataAdapter("SELECT * FROM REF_LONG WHERE SIMPLE_NR < 100; SELECT * FROM SIMPLE_LONG WHERE NR < 100", connection_);
  adapter.Fill(ds);
}

            using (FbConnection connection = new FbConnection(ConnectionString))
            {
                FbCommand command = connection.CreateCommand();
                command.CommandText = "EXECUTE BLOCK (PNr INTEGER = @PNr)"+
                                      "  as"+
                                      "  begin"+
                                      "  DELETE FROM ORDER_GOODS WHERE ORDER_NR = :PNr;"+
                                      "  DELETE FROM ORDERS WHERE NR = :PNr;"+
                                      "  end ";
                command.Parameters.AddWithValue("@PNr", aOrderNr);

                connection.Open();
                command.ExecuteNonQuery();
            }

            using (FbConnection connection = new FbConnection(ConnectionString))
            {
                FbCommand command = connection.CreateCommand();
                command.CommandText = "EXECUTE BLOCK as begin \r\n"+
                                                      "SELECT * FROM REF_LONG WHERE SIMPLE_NR < 100; \r\n"+
                                                      "SELECT * FROM SIMPLE_LONG WHERE NR < 100; \r\n"+
                                                     "end";
                connection.Open();
                command.ExecuteReader();
            }