A is correct, in shared UNDO mode, UNDO can exist in the CDB only.
B is wrong, because PDBs must be reopened to recognize the central UNDO C is wrong, because as the database is RAC and enabled with LOCAL UNDO, you need to assign specific Undo tablespace to each PDB on node-1 & node-2 by executing below commands.
On node-1:
alter system set undo_tablespace=UNDOTBS1 container=current sid='DBCDB1' scope=spfile; >>>> sid=First Instance On Node-2 alter system set undo_tablespace=UNDOTBS2 container=current sid='DBCDB2' scope=spfile; >>>> sid=Second Instance D is wrong, becuase as long as LOCAL UNDO used you cant create UNDO in PDB E is wrong, PDB UNDO tablespaces should be dropped after the change.
F is correct, when you change the undo mode of a CDB, the new undo mode applies to an individual container the first time the container is opened after the change.