Which three are true about block media recovery（）?
A、The target database for which one or more blocks are to be recovered must be in the OPEN state
B、The data file containing the block being recovered remains online
C、It cannot repair logical corruption
D、It can be performed on noncorrupt blocks
E、A block being recovered is not accessible
F、To use it, Flashback Database must be enabledhttp://www.cndba.cn/hbhe0316/article/108636http://www.cndba.cn/hbhe0316/article/108636http://www.cndba.cn/hbhe0316/article/108636

答案:BDE
当发生以下情况时，实例恢复无效，需要进行介质恢复：
– 数据文件丢失，损坏。
– 在线日志文件(online redo)丢失，损坏。
– 数据文件太旧 (比如从一个备份集中恢复过来的文件。)
–文件太新（比如，其它所有的文件都是从备份中恢复过来的）

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