Which statement is true regarding the backup of the TOOLS tablespace?

Consider the following scenario for your database:
– Backup optimization is enabled in RMAN.
– The recovery window is set to 7 days in RMAN.
– The most recent backup to disk for the TOOLS tablespace was taken on November 3, 2007.
– The TOOLS tablespace is read-only since November 4, 2007.
On November 23, 2007, you issue the RMAN command to back up the database to disk.
Which statement is true regarding the backup of the TOOLS tablespace?

A.
The RMAN backup fails because the TOOLS tablespace is read-only

B.
The RMAN skips the backup of the tablespace because backup optimization is enabled

C.
The RMAN makes backup because optimization can be enabled only for backups to disk

D.
The RMAN makes the backup because no backup of the tablespace exists within the seven day window

Explanation:
http://web.njit.edu/info/limpid/DOC/backup.102/b14191/rcmconc1008.htm
With a recovery window-based retention policy:
For backups to tape, RMAN takes another backup of a file, even if a backup of an identical file exists, if the most recent backup is older than the configured recovery window. This is done to allow media to be recycled after the media expires.
For backups to disk, RMAN skips taking the backup if an identical file is available from a backup on disk, even if that backup is older than the beginning of the recovery window. The retention policy causes RMAN to retain the old backup for as long as it is needed.