By default, there are two databases, template 0 and template 1.
※This sample exam is different from those that appear in the actual OSS-DB Exam.
When you create a database cluster with the initdb command, it creates three databases, a template database called template0 and template1, and a regular database called postgres.
By default, when creating a database with the createdb command or the SQL CREATE DATABASE statement, a copy of template1 is created by default, but you can specify other databases such as template0 by option.
Template0 is a read-only database that contains only system standard objects and can not be deleted. Database template1 can be written if necessary, and it is also possible to delete (DROP DATABASE) the database itself.
Postgres is an ordinary database that exists by default, and there are some third party products that assume its existence, but after all, even if you delete it, it is not a problem as a system.
Therefore, the correct answers are C and D.