Read the passage from History of the United States, by Charles and Mary Beard. As necessary to mechanical industry as steel and steam power was the great market, spread over a wide and diversified area and knit together by efficient means of transportation. This service was supplied to industry by the steamship, which began its career on the Hudson in 1807; by the canals, of which the Erie, opened in 1825, was the most noteworthy; and by the railways, which came into practical operation about 1830.

With sure instinct Eastern manufacturer reached out for the markets of the Northwest territory where free farmers were annually producing staggering crops of corn, wheat, bacon, and wool. The two great canal systems — the Erie, connecting New York City with the waterways of the Great Lakes and the Pennsylvania chain, which linked Philadelphia with the headwaters of the Ohio — gradually turned the tide of trade from New Orleans to the Eastern seaboard.

In a summary of this passage, which of the following could support a central trend?
steel
industry’s need for a market
the Erie canal system
the railways