Which three possible values can be set for the TIME_ZONE session parameter by using the ALTER SESSION command?

http://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_2012.htm

TIME_ZONE = ‘[+ | -] hh:mm’
TIME_ZONE = LOCAL
TIME_ZONE = DBTIMEZONE
TIME_ZONE = ‘time_zone_region’

SELECT FROM_TZ(TIMESTAMP ‘2000-03-28 08:00:00’, ‘-9:00’) FROM DUAL;
select day from dual;

select SESSIONTIMEZONE from dual;
ALTER SESSION SET TIME_ZONE = ‘-7:0’;
ALTER SESSION SET TIME_ZONE = ‘os’;
ALTER SESSION SET TIME_ZONE = local;
ALTER SESSION SET TIME_ZONE =’-8:20′;
ALTER SESSION SET TIME_ZONE = DBTIMEZONE;
ALTER SESSION SET TIME_ZONE = ‘Australia’;
ALTER SESSION SET TIME_ZONE = ‘Africa’;
ALTER SESSION SET TIME_ZONE = ‘America/New_York’;

select TZNAME from V$TIMEZONE_NAMES where TZNAME like ‘Australia’;
select TZNAME from V$TIMEZONE_NAMES where TZNAME like ‘America%’;
SELECT DBTIMEZONE FROM DUAL;

BCD