Which two are true about offloading backups to a physical standby database in a Data Guard environment?
A.
The standby database must be registered in an RMAN catalog after the primary database has been registered.
B.
The standby database cannot be registered in an RMAN catalog if the primary database has not been registered.
C.
Backups of the standby control file taken while connected to the catalog where the database is registered, may be used to restore the control file on the primary
database.
D.
The standby database must be registered in an RMAN catalog before the primary database has been registered.
Explanation:
Only the primary database must be explicitly registered using the REGISTER DATABASE command. You do this after connecting RMAN to the recovery catalog
and primary database as TARGET.https://docs.oracle.com/database/121/SBYDB/rman.htm#SBYDB4851
A, B
Backups of standby control files and nonstandby control files are interchangeable. For example, you can restore a standby control file on a primary database and a primary control file on a physical standby database. This interchangeability means that you can offload control file backups to one database in a Data Guard environment. RMAN automatically updates the filenames for database files during restore and recovery at the databases.
B, C is correct
the *must* in A is too strong
B,C