Before the US transportation infrastructure was built, raw materials and finished products were most efficiently transported and distributed by horse and buggy. through port cities. via trading posts. via navigable waterways.

The correct answer is C: through port cities.

via navigable waterways

Explanation:

Before the Industrial Revolution and the advances it brought in the transportation, the majority of the raw materials and finished products were mostly transported via navigable waterways. As there was not other efficient way to transport goods deeper into the mainland, since the railways were still not built, the larger rivers were of crucial importance. The larger rivers were navigable, and they were going deep into the mainland, which enabled the transportation of goods to be relatively easy, as well as on long distances.