The correct answer is A) factories.
After the Civil War, America began to develop industry more than it had before in any other time period. The United States would emerge as an industrial superpower during the late 19th and early 20th centuries. It would be during this time period that the United States had a majority of their labor force working in factories rather than farms. This had never happened before the Civil War. Now, at the end of the Gilded Age (1900's) the United States workforce was roughly 2/3rds factory workers.
