A: In a cumulative level 1 backup, RMAN backs up all the blocks used since the most recent level
0 incremental backup.
E: Oracle Block Change Tracking
Once enabled; this new 10g feature records the modified since last backup and stores the log of it in a block change tracking file using the CTW (Change Tracking Writer) process. During backups RMAN uses the log file to identify the specific blocks that must be backed up. This improves RMAN's performance as it does not have to scan whole datafiles to detect changed blocks.
Logging of changed blocks is performed by the CTRW process which is also responsible for writing data to the block change tracking file.
Note:
* An incremental level 0 backup backs up all blocks that have ever been in use in this database.

Explanation/Reference:
Explanation:
To perform operations on a single PDB, you can connect as target either to the root or directly to the PDB.
* (A) If you connect to the root, you must use the PLUGGABLE DATABASE syntax in your RMAN commands. For example, to back up a PDB, you use the BACKUP PLUGGABLE DATABASE command.
* (C)If instead you connect directly to a PDB, you can use the same commands that you would use when connecting to a non-CDB. For example, to back up a PDB, you would use the BACKUP DATABASE command.

Explanation/Reference:
Explanation:
http://docs.oracle.com/database/121/BRADV/flashdb.htm#BRADV529http://docs.oracle.com/ database/121/BRADV/glossary.htm#BRADV90169