Which one of the following descriptions best describes "horizontal integration"?

Horizontal integration is the acquisition of additional business activities that are at the same level of the value chain in similar or different industries. This can be achieved by internal expansion through a reinvestment of operating profits or by external expansion through a merger or acquisition (M&A). Since the different firms integrating are involved in the same stage of production, horizontal integration allows them to share resources at that level.

The theory is land mass basically what they said.