Firms that have several plants that produce the same or related products are said to be:

A) horizontally integrated.
B) vertically integrated.
C) conglomerates.
D) cooperatives.

Horizontal integration refers to the process of a company acquiring or merging with a similar or a competing company operating on the same level of the supply chain to increase its market share and achieve economies of scale. In this case, a firm that has several plants producing the same or related products can be said to be horizontally integrated.