The RECOVER STANDBY DATABASE FROM SERVICE command in RMAN is designed to automate various steps required to recover the standby database, especially when dealing with an archive gap. When this command is executed, the following actions can occur automatically:
Remember all data file names on the standby (1): RMAN has the capability to recall the names and paths of all data files associated with the standby database.
Restart standby in nomount (2): The standby database can be automatically restarted in the NOMOUNT state, allowing recovery operations to proceed without the database being open.
Restore controlfile from primary (3): RMAN can restore the control file from the primary database to the standby system, ensuring that the standby has the most up-to-date control file.
Mount standby database (4): After restoring the control file, the standby database is mounted to prepare for data file recovery.
Rename data files from stored standby names (5): Not typically done automatically by this command.
Restore new data files to new names (6): New data files added to the primary since the last synchronization can be restored to the standby with their correct names.
Recover standby (7): Finally, RMAN will apply any necessary redo logs to bring the standby database up to date with the primary.
While some steps, such as renaming data files (5), typically require manual intervention or scripting, most of the recovery process can be handled by RMAN automatically, streamlining the recovery of the standby database.
Reference:
Oracle Database Backup and Recovery User's Guide
Oracle Data Guard Concepts and Administration Guide

To increase the number of applier processes on a logical standby database, the following changes can be made:
C: Increasing the value for the MAX_SERVERS SQL apply parameter would allow for more applier processes to be initiated, assuming that system resources permit.
D: Increasing the PARALLEL_MAX_SERVERS initialization parameter would allow for more parallel execution processes, which can be used by SQL apply to increase the number of applier processes.
Option A is incorrect as decreasing the number of archiver processes will not necessarily increase the number of applier processes; these are unrelated components.
Option B is incorrect because the 'FREPARER' processes do not exist, it seems to be a typographical error, and the 'REPARER' is not a valid Oracle process or parameter.
Option E is incorrect because the RECOVERY_PARALLELISM parameter controls the number of processes used for instance recovery and media recovery, not for SQL apply.

* A fast recovery area must be configured (B): Flashback Database requires a fast recovery area to be set up because flashback logs are stored there. The fast recovery area is a unified storage location for all recovery-related files and activities.
* The database must be in ARCHIVELOG mode (C): Flashback Database operation relies on the ability to archive redo logs. Therefore, the database must be running in ARCHIVELOG mode for Flashback Database to be enabled.
References:
* Oracle Database Backup and Recovery User's Guide
* Oracle Data Guard Concepts and Administration Guide