I have tablespaces in 9i that i dont know what it is:

DRSYS
CWMLITE
EXAMPLE

i tried to drop EXAMPLE and it gives me ORA-23515 because it contains materialized views.
I know how to drop it
DROP TABLESPACE
INCLUDING CONTENTS
CASCADE CONSTRAINTS;

I just want to know if i can dropped them without causing trouble, cuse it was installed by
default with 9i?

Im asking this question because i almost drop the undo tablespace because i did not know what it was, and realise it was rollback tablespace.