Which two are true about the usage of DBMS_ROLLING? 

Answer options:

A. The leading group contains the original primary database.
B. The trailing group contains the original primary database.
C. The background process DMON must be enabled on all database instances that take part in the rolling release upgrade process.
D. At least one logical standby database must be part of the initial Data Guard configuration.
E. The trailing group can contain standby databases that will protect the original primary database during the rolling release upgrade process.

DE

E: The trailing group contains the original primary database and standby databases that will protect the original primary during the rolling upgrade process. D: Databases in the leading group are upgraded first; hence the name leading group. The leading group contains the designated future primary database, and the physical standbys that you can configure to protect the designated future primary. The future primary is first converted into a logical standby database and then the new database software is installed on it and the upgrade process is run. Other standby databases in the leading group also must have their software upgraded at this point. Note: To upgrade the database software in an Oracle Data Guard configuration in a rolling fashion, you first designate a physical standby as the future primary database. Conceptually, the rolling upgrade process splits the Oracle Data Guard configuration into two groups: the leading group (LG) and the trailing group (TG). Incorrect Answers: A: The leading group contains the designated future primary database, and the physical standbys that you can configure to protect the designated future primary. References: https://docs.oracle.com/database/121/SBYDB/dbms_rolling_upgrades.htm#SBYDB5431