DBA_SYS_PRIVS view - Exercise

One of your developers has come to you complaining that he cannot create objects in the USERS tablespace. Upon investigation, you find that there is no freespace left in USERS. Furthermore, you find that a user named JEFF has created several large tables in the tablespace. You did not think that JEFF had enough quota on the tablespace to create objects that large. Is it possible that JEFF holds the UNLIMITED TABLESPACE privilege?
Or does he just have a large quota. You need to find out what's going on.

Which things would you check to figure out why JEFF can use up so much space? If you are planning to query any of the data dictionary tables, write those queries out.