Moving Between Two Points on a PPF,a Country Gains 6

Multiple Choice

Moving between two points on a PPF,a country gains 6 automobiles and forgoes 3 trucks.The opportunity cost of 1 automobile is

A) 3 trucks.
B) 6 automobiles - 3 trucks.
C) 2 trucks.
D) 1/2 of a truck.
E) 1 automobile.