Under what circumstances will the residual supply curve for a country

Under what circumstances will the residual supply curve for a country be upward sloping?

A) when it does not import any of the good from the rest of the world
B) when it imports a small portion of the rest of the world’s supply of the good
C) when it imports a large portion of the rest of the world’s supply of the good
D) Either A or B

ANSWER

C