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You issue this SQL command to perform an online backup of the USER_DATA tablespace：ALTER TABLESPACE user_data BEGIN BACKUP；Next， you issue an operating system command to back up user_data01.dbf， the file that belongs to the USER_DATA tablespace. You then experience an instance failure.  Which three statements are true？（）
A:A
B:B
C:C
D:D
E:E

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出自：Oracle认证

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