Explanation/Reference:
References: https://docs.oracle.com/database/121/LADBI/oraclerestart.htm#LADBI999

* The choice of threading model is dictated by the THREADED_EXECUTION initialization parameter.
THREADED_EXECUTION=FALSE : The default value causes Oracle to run using the multiprocess model.
THREADED_EXECUTION=TRUE : Oracle runs with the multithreaded model.
* OS Authentication is not supported with the multithreaded model.
* THREADED_EXECUTION
When this initialization parameter is set to TRUE,which enables the multithreaded Oracle model, operating system authentication is not supported. Attempts to connect to the database using operating system authentication (for example, CONNECT / AS SYSDBA or
CONNECT / ) when this initialization parameter isset to TRUE receive an ORA-
01031"insufficient privileges" error.
F: The new SET CONTAINER statement within a call back function:
The advantage of SET CONTAINER is that the pool does not have to create a new connection to a PDB, if there is an exisitngconnection to a different PDB. The pool can use the existing connection, and through SET CONTAINER, can connect to the desired PDB.
This can be done using:
ALTER SESSION SET CONTAINER=<PDB Name>
This avoids the need to create a new connection from scratch.

Explanation/Reference:
Explanation:
C (not D): CONS_VPD_AUTO
Used to indicate to copy VPD policies automatically
* DBMS_RLS.ADD_POLICY
/ The DBMS_RLS package contains the fine-grained access control administrative interface, which is used to implement Virtual Private Database (VPD).DBMS_RLS is available with the Enterprise Edition only.
Note:
* CONS_USE_PK and CONS_USE_ROWID are constants used as input to the "options_flag" parameter in both the START_REDEF_TABLE Procedure and CAN_REDEF_TABLE Procedure.
CONS_USE_ROWID is used to indicate that the redefinition should be done using rowids while CONS_USE_PK implies that the redefinition should be done using primary keys or pseudo-primary keys (which are unique keys with all component columns having NOT NULL constraints).
* DBMS_REDEFINITION.START_REDEF_TABLE
To achieve online redefinition, incrementally maintainable local materialized views are used. These logs keep track of the changes to the master tables and are used by the materialized views during refresh synchronization.
* START_REDEF_TABLE Procedure
Prior to calling this procedure, you must manually create an empty interim table (in the same schema as the table to be redefined) with the desired attributes of the post-redefinition table, and then call this procedure to initiate the redefinition.

Explanation/Reference:
Explanation:
AB: You can make individual table columns invisible. Any generic access of a table does not show the invisible columns in the table. For example, the following operations do not display invisible columns in the output:
* SELECT * FROM statements in SQL
* DESCRIBE commands in SQL*Plus
* %ROWTYPE attribute declarations in PL/SQL
* Describes in Oracle Call Interface (OCI)
Incorrect:
Not D: You can make invisible columns visible.
You can make a column invisible during table creation or when you add a column to a table, and you can later alter the table to make the same column visible.
References: