As part of a manual upgrade of your database to Oracle Database 12c, you plan to issue the command: SQL> STARTUP UPGRADE Which three statements are true about the upgrade process? (Choose three.)

During the `STARTUP UPGRADE` process, Oracle automatically disables all system triggers to prevent them from interfering with the execution of upgrade scripts and to ensure a controlled upgrade environment.

When a database is started in `UPGRADE` mode, most database objects are in an inconsistent state or are being modified, making only queries on fixed views (e.g., V$ views) guaranteed to execute without errors until the `catctl.pl` script completes the upgrade.

The `COMPATIBLE` initialization parameter must be set to at least '12.1.0' prior to issuing the `STARTUP UPGRADE` command to enable Oracle Database 12c features and ensure successful upgrade completion.

Job queues are typically disabled or quiesced during a database upgrade to prevent background jobs from running and interfering with the upgrade process, which could cause errors or data corruption.

While `SYSDBA` connections are primarily used for database upgrades, the statement 'only connections AS SYSDBA are allowed' is an oversimplification; the database is in a restricted state, but the restriction is more about schema objects than connection type.