※This sample exam is different from those that appear in the actual OSS-DB Exam.
The system catalog contains information about various objects in the database.
pg_class contains information about the table and objects (views, sequences, materialized views) related to the table(having column).
Information about the columns of the table is stored in the system catalog named pg_attribute, and one row is created in pg_attribute for one column.
Names starting with other pg_s in the choice may seem to be likable, but there are only two system catalogs, pg_class and pg_attribute. pg_tables provides some useful information about the table, but it is called a system view and it is a view that combines multiple system catalogs. Others do not exist on the system.
Therefore, the correct answer is C.
For details of each system catalog, please refer to https://www.postgresql.org/docs/9.5/static/catalogs.html.