Explanation:
This command will switch the database from the standby to the primary role. This statement ensures that all redo log files have been received and that they have been applied up to the endof- redo marker. It also converts the standby control file to the current control file.
Incorrect Answers:
1: This command just mounts the database as a standby database.
2: This command backs up the control file.
4: This command closes the primary database, completes the archive task, inserts an end-ofredo marker, and backs up the current control file to the SQL session trace file for conversion to a standby control file.
Reference:
OCP Oracle9i Database: New Features for Administrators, Daniel Benjamin, p. 51-74
Chapter 2: Availability Enhancements
Oracle 9i New Features, Robert Freeman, p. 86-99
Chapter 3: New Oracle9i Availability and Recoverability Features

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