He created a trust that controlled 90% of the nation's oil refineries. If I remember correctly, horizontal integration is when you buy out the other businesses in the same market, while vertical integration is where you take control of everything related to your product, which is getting the oil, refining it, and distributing it, rather than selling those tasks out to third parties.
I believe the answer is most definitely A and if not that it is B, the other two I know for sure are wrong, hope this helps!!
Disease. The Europeans got greedy and sent Native Americans objects, mostly blankets, with disease on them.
