Explanation/Reference:
Explanation:
Step 1 (1) : To copy tablespaces from one database to another using transportable tablespace, the source tablespaces are first kept in READ-ONLY mode (to ensure data consistency). Once the tablespaces are in READ-ONLY mode, the actual datafiles belonging to the source tablespaces are copied from source database to target database (using any available methods like scp, sftp, rcp, etc).
Step 2 (2): Once the tablespace is kept in READ-ONLY mode, we need to generate the metadata export of the tablespaces that needs to transported using the DataPump export utility.
Step 3 (4): Once the metadata export is generated on the source database for all the tablespaces that needs to be transported, we need to copy the Export Dump file as well as all the datafiles belonging to the tablespaces to be transported to the target database server.
References: http://www.oraclebuffer.com/oracle/migrate-oracle-database-using-transportable-tablespace/

Explanation/Reference:
Explanation:
Reference:
http://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmcncpt.htm#BRADV89481 (See unused block compression)
https://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmcncpt.htm#BRADV89481

Reference:http://www.oracle.com/technetwork/database/focus-areas/storage/total-recallwhitepaper-171749.pdf(page 8)

Explanation/Reference:
Explanation:
When RMAN performs active database duplication using backup sets, a connection is established with the source database and the auxiliary database. The auxiliary database then connects to the source database through Oracle Net Services and retrieves the required database files from the source database. This method of active database duplication is also to as the pull-based method.
Example:
DUPLICATE TARGET DATABASE TO dupdb
FROM ACTIVE DATABASE
PASSWORD FILE
SPFILE
NOFILENAMECHECK;
Incorrect Answers:
A, B, D: When active database duplication is performed using image copies, after RMAN establishes a connection with the source database, the source database transfers the required database files to the auxiliary database. Using image copies may require additional resources on the source database. This method is referred to as the push-based method of active database duplication.
References: https://docs.oracle.com/database/121/BRADV/rcmdupdb.htm