The correct answer is A. Many cities became industrial centers
Step-by-step explanation:
In the United States, multiple railroads were built from the 19th century to the end of the 20th century, indeed during these years, railroads systems were created to connect important cities and towns. This supported the economic growth and industrialization of the country as raw materials and manufactured products could be transported faster and also, workers could get into the cities.
Besides this, due to railroads, many cities began expanding as more people moved to urban areas and also many cities became industrial centers due to the economical grown and industrialization during this time. Thus, it can be concluded railroads had a great impact on cities in the U.S. because due to these "many cities became industrial centers".