Which factor contributed to the formation of large corporations during the late 19th century?

AProduction could be organized more efficiently on a larger scale.
BWage levels could be increased when employing a smaller number of workers.
CBusinesses could only export to foreign markets with a large amount of capital.
DGovernment support for businesses was more likely in a highly concentrated industry.

(If someone could please help I have a feeling it's either A or B but I'm very unsure and I've looked through all my notes for school to figure this out. )

Corporations arose through an increase in industrialization with large-scale agriculture and greater manufacturing and production output. These corporations tapped into natural resources and began to utilize methods that allowed them to maintain and grow their power. One method created by Swift was vertical integration in which a company controlled every aspect of their industry, from the raw materials to the advertising of the finished products.

These large firms then used techniques like predatory pricing to drive their competitors out of business. Rockefeller pioneered horizontal integration in which he forced local companies to merge unto his conglomerate, allowing him to create a trust, monopolizing the entire oil refining industry.