60、Which two are true about UNDO data?
A. Inactive UNDO is never written to disk.
B. Active UNDO is always kept in memory
C. Only DML statements generate UNDO.
D. Active UNDO can never be overwritten.
E. It can be used to restore a table by using FLASHBACK TABLE.
F. Inactive UNDO cannot be overwritten until the elapsed time since becoming inactive exceeds UNDO RETENTION.
Correct Answer: DE
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原文：https://www.cnblogs.com/alice9313/p/9661358.html