Which of the following criteria was a key milestone for the object$-$relational model created in the mid$-1980$s$?$ A$)$ The creation of a single structure that contained both data and its relationships B$)$ Identification of all of the data to be stored in a collection of tables with each table being independent and each of the rows in a table being related by common values C$)$ The existence of support for unstructured data D$)$ The use of this data model on IBM mainframe systems