Which statement is true regarding undo management in a RAC environment?

Which statement is true regarding undo management in a RAC environment?

A.
It is possible to store undo tablespaces on nonshared disks.

B.
A RAC database contains one undo tablespace shared by all instances.

C.
A RAC database must have defined only one undo tablespace for each instance.

D.
You cannot mix automatic undo management and manual undo management.