The DBMS_COMPARISON package, used for comparing and converging data objects within a single database or between databases, requires that the databases involved in the block comparison be at least mounted (A). This allows the procedure to access the data blocks for comparison. Additionally, the progress of long-running operations such as block comparison can be monitored using the dynamic performance view V$SESSION_LONGOPS (D), which provides information on the operation's progress and estimated completion time.
Reference:
Oracle Database PL/SQL Packages and Types Reference provides comprehensive details on the DBMS_COMPARISON package, including its procedures and how to monitor their progress. Additionally, Oracle Database Reference explains the V$SESSION_LONGOPS view, which is commonly used for monitoring long operations in the database.

Based on the Oracle Database 19c documentation, the correct answers about SQL Apply filters for a logical standby database are:
A). They can be used to skip execution of DML triggers on a table while allowing the DML to execute.
B). They can be used to skip CREATE TABLE commands.
C). They can be used to skip ALTER SYSTEM and ALTER DATABASE commands.
G). They can be used to skip ALTER TABLE commands on specific tables.
Comprehensive Detailed Explanation:
SQL Apply filters in a logical standby database can be set to control which SQL operations are applied to the standby. These filters allow for certain commands to be skipped, ensuring that they do not impact the standby database. For example, filters can be used to skip the execution of DML triggers to prevent them from firing during SQL Apply, while still allowing the underlying DML to be executed on the logical standby database. This is particularly useful when certain triggers are not desired to run in a standby environment. CREATE TABLE, ALTER SYSTEM, ALTER DATABASE, and specific ALTER TABLE commands can also be skipped using SQL Apply filters to prevent unwanted structural changes or administrative operations from affecting the logical standby database. These capabilities provide a level of control to ensure that the logical standby database reflects only the desired state of the primary database.
Reference:
Oracle Database SQL Language Reference and Oracle Data Guard Concepts and Administration guide offer comprehensive details on the use of SQL Apply filters, including the range of SQL statements that can be influenced by these filters in a logical standby database environment.