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Which two statements are true regarding undo tablespaces（）
A:The database can have more than one undo tablespace.
B:The UNDO_TABLESPACE parameter is valid in both automatic andmanualundo management.
C:Undo segments automatically grow and shrink as needed， acting as circular storage buffer for their assigned transactions.
D:An undotablespaceis automatically created if the UNDO_TABLESPACEparameter is not set and the UNDO_MANAGEMENT parameter is set to AUTO during the database instance start up.

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出自：Oracle认证

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