What is true if you want to switch undo tablespaces from the current one， called UNDO1， to a new one called UNDO2？（）

A.It is NOT possible to switch unless no active transaction exist in UNDO1.

B.It is possible to switch to UNDO2； but current active transactions will abort.

C.It is possible to switch to UNDO2； current active transactions will be automatically migrated to UNDO2.

D.It is possible to switch to UNDO2； only current active transactions will continue to execute inside UNDO1.