What is the author's attitude toward the "railroad novels" and other books about railroads written between 1890 and 1920

A．They have as much literary importance as the books written by Emerson, Thoreau, and Adams.
B．They are good examples of the effects industry and business had on the literature of the United States.
C．They contributed to the weakening of traditional values.
D．They are worth reading as sources of knowledge about the impact of railroads on life in the United States.