Which of the Following Is the Best Example of a Voluntary

Which of the following is the best example of a voluntary export restraint?

A) a limit imposed by the U.S. government on the number of cell phones that the United States can import from Korea
B) a subsidy granted by the U.S. government to domestic cell phone manufacturers so they can compete more effectively with foreign cell phone manufacturers
C) a limit set by the Korean government on the number of cell phones that the United States can import fro Korea.
D) a $50 per-cell phone-fee imposed on all cell phones vehicles imported into the United States