D. Expansion of railroads caused industry to grow during the Second Industrial Revolution.
The Second Industrial Revolution, which took place from the late 19th century to the early 20th century, was characterized by the growth of new industries such as steel, chemicals, and electricity. One of the major factors that contributed to this growth was the expansion of railroads, which allowed for faster and more efficient transportation of goods and raw materials. The railroads made it possible for factories to be located farther away from city centers and ports, and allowed for the development of new markets.