Ordering query results

I have the following query.

Ordering the query gives me error:
ORA-01791: not a SELECTed expression

How do i order this query, first by colB, colC and ColA.

SELECT DISTINCT exch.colA  ||'|'|| hol.colB  ||'|'|| exch.colC
    FROM (  SELECT bc.colA,
                   bc.colB,
                   ex.colC,
              FROM tabA bc, tabB ex
             WHERE AND bc.colA IS NOT NULL
                   AND ex.colB = bc.colB
                   AND ex.colB IS NOT NULL
          GROUP BY bc.colA,
                   bc.colB,
                   ex.colC,
          ORDER BY bc.colA) exch,
         (SELECT *
            FROM tabA
           WHERE AND dt IS NOT NULL
                 AND dt >= TRUNC(TO_DATE ('09-JUL-10', 'dd-mon-yy'),'MONTH')
                 AND day_type = 'Myday') hol
   WHERE hol.colA = exch.colA
   ORDER BY exch.colA; <-- error on ordering