The correct answer is C) union activism.
What decreased steadily during the Second Industrial Revolution was union activism.
In the history of the United States, the Second Industrial Revolution was the industrialization time from 1870 to 1914. During this time, manufacturing plants and businesses focused on developed different industries compared with the First Industrial Revolution. In the first one, fabrics manufactured raw materials and natural resources such as cotton or tobacco. In the second one, the oil industry was developed as well as the steel industry. Railroads played a key role in the development of these industries because efficient transportation was needed to trade products. During this period urbanization grew, the population fled to the larger cities where the manufacturing plants were located, and union activism decreased.