After the Civil War, the United States: a - became more industrial
b - made advancements in communication and transportation.
c - grew to be one of the world's wealthiest countries.
d - All of the choices are correct.

D All of the choices are correct.

i guess it should be d option i en all of the above

because its important to learn about other countries and how high tech they are compared to us. also its good to learn about other cultures and how ours differs and in common also we need to learn about companies that we still buy since they ship it here.