Final answer:
The question is about identifying a column store database from a list of options. However, none of the options provided (Cassandra, Riak, MongoDB, Redis) are column store databases, but they represent other types of NoSQL databases.
Step-by-step explanation:
The question asks which of the provided options is a column store database. None of the databases listed in the options are column-based stores; rather, they are examples of other types of NoSQL databases. Cassandra, for instance, is a wide-column store, which is a type of NoSQL database that uses tables, rows, and dynamic columns to manage data. Riak is a distributed key-value store. MongoDB is a document-oriented database, and Redis is an in-memory key-value store.