Which action should you perform immediately after using this command?

The database is running in the ARCHIVELOG mode. It has three redo log groups with one
member each. One of the redo log groups has become corrupted. You have issued the following
command during the recovery of a damaged redo log file:
ALTER DATABASE CLEAR UNARCHIVED LOGFILE GROUP 3;
Which action should you perform immediately after using this command?

A.
You should perform a log switch

B.
You should make a backup of the database

C.
You should switch the database to the NONARCHIVELOG mode

D.
You should shut down the database instance and perform a complete database recovery

Explanation:
SQL> ALTER DATABASE CLEAR LOGFILE UNARCHIVED GROUP 3;
Immediately back up all datafiles in the database with an operating system utility, so that you have
a backup you can use for complete recovery without relying on the cleared log group. For
example, enter:
% cp /disk1/oracle/dbs/*.dbf /disk2/backup

http://www.oracle-dba-online.com/managing_redo_logfiles.htm
This statement clears the corrupted redo logs and avoids archiving them. The cleared redo logs
are available for use even though they were not archived. If you clear a log file that is needed for
recovery of a backup, then you can no longer recover from that backup. The database writes a
message in the alert log describing the backups from which you cannot recover.