What does the DB_FLASHBACK_RETENTION_TARGET parameter configure?（）

A. n upper limit on how far you can flash back the database, depending on the information in the redo logs

B. n upper limit on how far you can flash back the database, depending on the information in the undo tablespace

C. The amount of time for which the flashback data is to be kept in the flash recovery area, provided that there is enough space

D. The amount of time for which the flashback data is guaranteed to be kept in the undo tablespace, provided that there is enough space