[单选题]Your database is running under automatic undo mana

AThe extents in undo tablespace retain data until the next full database backup.

BThe extents containing committed data in the undo tablespace are never overwritten.

CThe extents which no longer contain uncommitted data in the undo tablespace are not overwritten for at least15 minutes.

DThe extents containing committed data in the undo tablespace are not overwritten until the instance is shut down.