Answer;
D.constructed vast networks of railroads.
After Germany’s unification in 1871, industrialization accelerated and constructed vast networks of railroads.
Explanation;
After the Unification of Germany under Otto von Bismarck, industrialization followed after. Germany then created Zollverein. Zollverein is a free trade organization between the German States.
The unification provided a base platform for industry to grow, and Bismarck cared for this well. He implemented several policies to protect the baby business ; among them were laws which forced up the cost of many foreign items and made the German goods better value.
They were able to grow well after infrastructure improved, thus the start of inventing locomotive, which led to the high demand of metals like and coal. They were able to import and export their products and thus improved their agriculture