Which program is an example of domestic policy?

a.) nafta
b.) the versailles treaty
c.) the carter doctrine
d.) the clean air act
e.) nato

the american rail road was the most influential and useful transportation system developed in the 1800's with steam locomotives and in the very late 1800's and early 1900's diesel electric locomotives being used to transport goods and people around the newly expanded united states!

i dont know but i need points