Which two statements are true regarding undo tablespaces?

Which two statements are true regarding undo tablespaces? (Choose two.)

A.
The UNDO_TABLESPACE parameter is valid in both automatic and manual undo
management

B.
Undo segments automatically grow and shrink as needed, acting as circular
storage buffer for their assigned transactions

C.
The database can have more than one undo tablespace

D.
An undo tablespace is automatically created if the UNDO_TABLESPACE
parameter is not set and the UNDO_MANAGEMENT parameter is set to AUTO during
the database instance start up