Which of the following is likely to be the most effective trade restrictions?

Question

a) Tariffs

b) Import Quotas

c) Voluntary restrictions

d) Custom duties

Answer 1

I think "A" is right. Next would go "B".

Answer 2

Traditionally, the United States maintained an average 40% ad valorum tariff on manufactured imports from 1789 until about 1970.  

It should be noted that this period of time resulted in the United States becoming the most powerful, most free, and most prosperous nation in world history, and it happened in the shortest period of time ever recorded.  

As an added benefit, until the 20th century, the United States did not even have a need for income tax, choosing instead to fund government completely on the backs of foreign profit making corporations.