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The BOOKINGS table contains online booking information. When a booking is confirmed, the details are transferred to an archival table BOOKINGS_HIST and deleted from the BOOKINGS table. There is no fixed time interval between each online booking and its confirmation. Because sufficient space is not always available from the delete operations the high-water mark (HWM) is moved up and many rows are inserted below the HWM of the table. The BOOKINGS table has Automatic Segment Space Management(ASSM) and row movement enabled. The table is accessible in 24x7 mode.
What is the most efficient method to reclaim the space released by the delete operations in the BOOKINGS table?
A. Perform EXPORT, DROP, and IMPORT operations on the BOOKINGS table sequentially
B. Shrink the BOOKINGS table by using the ALTER TABLE... SHRINK SPACE command
C. Move the BOOKINGS table to a different location by using the ALTER TABLE... MOVE command
D. Deallocate the space in the BOOKINGS table by using the ALTER TABLE ... DEALLOCATE UNUSED command

AC 错误，由于数据库是 7*24 小时的，不能使用导出导出的方式重建表。也不能是 move 的方式移动表到其他位置，这样操作会丢失数据
D 错误，这种方式不能释放高水位之下的空间，只能使用高水位之上未使用的空间