Explanation
B: The seed is always read-only.
D: Pluggable databases can be started and stopped using SQL*Plus commands or the ALTER PLUGGABLE DATABASE command.

*You can include the CONTAINER clause in several SQL statements, such as the CREATE USER, ALTER USER, CREATE ROLE, GRANT, REVOKE, and ALTER SYSTEM statements.
* * CREATE ROLE with CONTAINER (optional) clause
/CONTAINER = ALL
Creates a common role.
/ CONTAINER = CURRENT
Creates a local role in the current PDB.

Explanation/Reference:
Explanation:
The alert log is a chronological log of messages and errors, and includes the following items:
All internal errors (ORA-600), block corruption errors (ORA-1578), and deadlock errors (ORA-60) that

occur
Administrative operations, such as CREATE, ALTER, and DROP statements and STARTUP,

SHUTDOWN, and ARCHIVELOG statements
Messages and errors relating to the functions of shared server and dispatcher processes

Errors occurring during the automatic refresh of a materialized view

The values of all initialization parameters that had nondefault values at the time the database and

instance start
Note:
* The alert log file (also referred to as the ALERT.LOG) is a chronological log of messages and errors written out by an Oracle Database. Typical messages found in this file is: database startup, shutdown, log switches, space errors, etc. This file should constantly be monitored to detect unexpected messages and corruptions.

Explanation/Reference:
Explanation:
RMAN> select name,open_mode from v$pdbs;
using target database control file instead of recovery catalogNAME OPEN_MODE
---------- ----PDB$SEED READ ONLYORA12P1 READ WRITEORA12P2 MOUNTED
RMAN> backup tablespace ora12p2:users;
Starting backup at 31-MAR-14allocated channel: ORA_DISK_1channel ORA_DISK_1: SID=137 device type=DISKchannel ORA_DISK_1: starting full datafile backup setchannel ORA_DISK_1: specifying datafile (s) in backup setinput datafile file number=00013 name=/appl/oradata/cdbroot/ORA12C1/ F5D05369C4B23E83E0430100007F6D99/datafile/o1_mf_users_9mhr0o5l_.dbfchannel ORA_DISK_1:
starting piece 1 at 31-MAR-14channel ORA_DISK_1: finished piece 1 at 31-MAR-14piece handle=/appl/ oradata/flash_recovery/ORA12C1/F5D05369C4B23E83E0430100007F6D99/backupset/2014_03_31/ o1_mf_nnndf_TAG20140331T001832_9mhzdb6w_.bkp tag=TAG20140331T001832
comment=NONEchannel ORA_DISK_1: backup set complete, elapsed time: 00:00:01Finished backup at
31-MAR-14
Starting Control File and SPFILE Autobackup at 31-MAR-14piece handle=/appl/oradata/flash_recovery/ ORA12C1/autobackup/2014_03_31/o1_mf_s_843610715_9mhzdcv8_.bkp comment=NONEFinished Control File and SPFILE Autobackup at 31-MAR-14
RMAN>
The above example illustrates that if root container is open and in archivelog it can do the backup of tablespace whether the pdb is mounted or open.