You work as a database administrator for Certkiller .com. The UNDO_RETENTION parameter in your database is set to 1000 and undoretention is not guaranteed. Which statement regarding retention of undo data is correct？（）

A. Undo data becomes obsolete after 1，000 seconds.
B. Undo data gets refreshed after 1，000 seconds.
C. Undo data will be stored permanently after 1，000 seconds.
D. Committed undo data would be retained for 1，000 seconds if free undo space is available.
E. Undo data will be retained in the UNDOtablespacefor 1，000 seconds， then it gets movedmovedto the TEMPORARYtablespaceto provide read consistency.