题目：
Which three statements are true about Flashback Database?
A. Flashback logs are written sequentially, and are archived.
B. Flashback Database uses a restored control file to recover a database.
C. The Oracle database automatically creates, deletes, and resides flashback logs in the Fast Recovery Area.
D. Flashback Database can recover a database to the state that it was in before a reset logs operation.
E. Flashback Database can recover a data file that was dropped during the span of time of the flashback.
F. Flashback logs are used to restore to the blocks’ before images, and then the redo data may be used to roll forward to the desired flashback time.
Answer: CDF
【解析】
闪回数据库使用其自己的日志记录机制，创建闪回日志并将其存储在快速恢复区域中。如果闪回日志可用，则可以使用闪回数据库。要利用此功能，必须预先设置数据库以创建闪回日志。闪回日志不进行归档。
当您使用闪回数据库将数据库后退到过去的目标时间时，该命令将确定在目标时间之后更改了哪些块，并从闪回日志中恢复它们。数据库将还原目标时间之前的每个块的版本。然后，数据库使用重做日志重新应用在将这些块写入闪回日志之后所做的更改。