Which of the Following Factors Occurred near the End of the Nineteenth

Which of the following factors occurred near the end of the nineteenth century and was most responsible for accelerating the usage of print ads by manufacturers who wished to sell their products?

A) The nation had not been in a war for over thirty years.
B) The advertising agency had become a reality.
C) Newspaper ads were relatively inexpensive.
D) The nation had reached a 90 percent literacy rate.
E) English was the established language of the United States.