Which reason for trade barriers is being used when the us refuses to trade with another country because they use child labor to manufacture goods? national security upholding standards protection of us jobs protection of us markets

How did inca develop their road system? a) they used mortar to hold the stones together.b) they built suspension bridges over rivers. c) they mixed copper and stone together to make the blocks.d) they laid roads in the cities, not in the less densely populated deserts.