Migration between North Korea and South Korea has been prohibited since the end of the Korean War in 1953. South Korea is now much richer than North Korea and has a much higher marginal product of labor and a much higher wage rate than North Korea. If workers could migrate from North Korea to South Korea, we would expect: 

a. Output to fall in South Korea but rise in North Korea.

b. Output to rise in each country.

c. Total combined output in the two countries to fall.

d. Total combined output in the two countries to rise.