PLEASE HELP!
The graph below compares the size of the urban and rural population in the United States during the first four decades of the 20th century:

Which of the following might explain the information contained in both graphs?

a. Problems with the Homestead Act resulted in a decline in rural population.
b. Increased immigration led to a rise in both urban and rural population.
c. Increased employment opportunities led to a rise in urban population.
d. Improvements in farming technology led to a decrease in rural population.