The case for the relational database

• A

  Document, because each entity can hold its related data nested inside it

• B

  Key-value, because every entity already has an id that can serve as the key

• C

  Column-family, because the reports are analytical in nature and read only a handful of columns across a very large number of rows

• D

  Relational, because the queries are not known in advance and joins answer new questions without a migration