In which situation can you use Flashback Database? 

Answer options:

A. when undoing a shrink data file operation
B. when retrieving a dropped tablespace
C. when returning to a point in time before the restoration or re-creation of a control file
D. when returning to a point in time before the most recent open resetlogs operation

B

Reference: http://docs.oracle.com/cd/B28359_01/backup.111/b28273/rcmsynta023.htm (prerequisites, third para) http://docs.oracle.com/cd/B28359_01/backup.111/b28273/rcmsynta023.htm#RCMRF194