You will have to examine how the question is worded. By default 11g will create all three tablespaces. You can however create a database with only SYSTEM and SYSAUX. Technically speaking you can upgrade pre-10g database and not add SYSAUX, or remove the SYSAUX tablespace after the database is created and therefore have a database with only a SYSTEM tablespace, but you would be ill advised to do so and I really don't think they would look for that in an answer.
From the 11.2 Administration Guide:
The SYSAUX tablespace is always created at database creation.
From another section of the Administration Guide:
An auto-extending undo tablespace named UNDOTBS1 is automatically
created when you create the database with Database Configuration
Assistant (DBCA)...
If no undo tablespace is available, then the
instance starts without an undo tablespace, and undo data is written
to the SYSTEM tablespace. You should avoid running in this mode.
From the 10.2 Concepts Guide:
...the SYSAUX tablespace is always created during database creation or
database upgrade...
During normal database operation, the Oracle database server does not
allow the SYSAUX tablespace to be dropped or renamed. Transportable
tablespaces for SYSAUX is not supported.
Note: If the SYSAUX tablespace is unavailable, such as due to a media
failure, then some database features might fail.
From the 10.1 SQL Reference:
You cannot drop the SYSTEM tablespace. You can drop the SYSAUX
tablespace only if you have the SYSDBA system privilege and you have
started the database in MIGRATE mode.
From the 10.1 Administrators Guide:
If the SYSAUX tablespace becomes unavailable, core database
functionality will remain operational. The database features that use
the SYSAUX tablespace could fail, or function with limited capability.
http://oradbpedia.com/wiki/The_SYSAUX_Tablespace has this take:
The SYSAUX tablespace is a new tablespace that is required in Oracle
Database 10g...
When you migrate to Oracle Database 10g, the SYSAUX tablespace needs
to be created as a part of that migration. This is done after mounting
the database under the new Oracle Database 10g database software. Once
you have mounted it, open the database in migrate mode with the
startup migrate command. After the database is open, you can create
the SYSAUX tablespace.
Note: The loss of the SYSAUX tablespace is not fatal to your database.
In our testing it appears that the only real impact is that certain
functionality related to the occupants of the SYSAUX tablespace is
lost.
Earlier versions did not have a SYSAUX tablespace:
SYSAUX is the name of the compulsory tablespace, introduced in Oracle
10g.
It's not actually possible to specify a different tablespace when importing using the oracle imp utility. However, as a workaround, you can pre-create the tables by doing a ROWS=N import into the USERS tablespace, then alter table mytable move tablespace BLOG_DATA; for each table to move them to the new tablespace, then do the import again with the IGNORE=Y parameter to ignore the table creation errors and import all of the data.
If the data was exported using Data Pump (expdp), (as an aside, everyone should be using this these days, rather than the old legacy exp/imp utilities) you can easily import into another tablespace using the REMAP_TABLESPACE parameter.
eg:
impdp scott/tiger@ZOMG file=blog_data.dmp directory=mydir remap_tablespace=USERS:BLOG_DATA
Best Answer
A default tablespace is just that, a default. If you specify a different tablespace when you create a table, the table will be created in the tablespace you specified. Though it would generally not make sense to do so, you could put each table in a different tablespace so that the user owned 20 tables in 20 different tablespaces none of which were the default tablespace.
Alternately, a user's default tablespace can be changed so it is possible that the 20 tables were created without a specified tablespace but when the user's default tablespace was different. Then the user's default tablespace was changed after all the tables were created.