What changes did railroads bring to American society during the Gilded Age?

A) The introduction of railroads lowered expectations in regard to when products would be available.
B) Because trains transported large numbers of people west, the population in the United States was rapidly decreasing.
C) The introduction of railroads marked the end of what is sometimes called the "second industrial revolution."
D) The introduction of railroads enabled a national market for goods and led to the creation of time zones.
E) Railroad lines only went west to east and east to west, so the northern economy suffered.