单项选择题
A.You can perform online whole database backups.
B.You can performofflinewhole database backups.
C.You cannot perform schema-level export/import operations.
D.You can perform the backup of only the SYSTEM tablespace when the database is open.
多项选择题 WhichtwostatementsaretrueabouttheAutomaticWorkloadRepository（AWR）（）
单项选择题 View the Exhibit and examine the attributes of an undo tablespace. In an OLTP system, the user SCOTT has started a query on a large table in the peak transactional hourthat performs bulk inserts. The query runs for more than 15 minutes and then SCOTT receives thefollowing error: ORA-01555: snapshot too old What could be the reason for this error（）