Companies such as Carnegie Steel in the 1890s often used vertical integration to increase profits. What does it mean to say that a company is vertically integrated?

A)
It has a monopoly in the marketplace on the product it creates.
B)
It operates in many different industries that make unrelated products.
C)
It combines all of the different stages of production in the same facility.
D)
It owns the supply of materials and services it needs to create its product.