Which two statements are true about undo segments and the use of undo by transactions in an Oracle database instance? （AC） A、Undo segments can to the first extent when a transaction fills the last extend of the undo segment. B、Undo segments can be stored in the SYSTEM tablespace. C、Undo segments can extend when a transaction fills the last extent of the undo segment. D、Undo segments can be stored in the SYSAUX tablespace. E、A single transaction may use multiple undo segments simultaneously