The Fox Entertainment Group counts among its assets a thriving TV production unit, a Hollywood movie studio, $33$ TV stations, a half$-$dozen national cable networks, and $21$ regional sports networks. Since most of the shows produced at its TV production unit and many of the movies made at its studio are made just for televising on its cable networks, Fox Entertainment Group is an example of a$($n$)$:

a$)$ integrated marketing system.

b$)$ corporate vertical marketing system.

c$)$ contractual vertical marketing system.

d$)$ corporate horizontal marketing system.