Which of the Following Is True

Which of the following is true?

A) The completion of the transcontinental railroad system in the 1880s eventually made the United States the world's first mass market.
B) Southern manufacturers were hurt by the high protective tariffs of the 19th century that kept out cheaper British manufactured goods.
C) The national railroad network created an "American economy" rather than just a series of regional economies located in one country.
D) Agricultural inventions such as John Deere's steel plows greatly improved farm productivity.
E) All of the choices are truE.