They aren't types of database, factor - they are types of relationships between the various datatables within a database.
Types of database would typically relational, navigational, hierarchical etc...
There are 2 main types, Hierarchical (IDMS for example) and relational (DB2 for example) however the original 12 requirements defined by Codd have not been achieved in any database so one could argue that the correct answer is 0.