Dent ‘n’ Scratch Used Cars and Trucks employs 3 salesmen. Data for their sales last month are shown in this table: Based on last month’s data, Joe’s opportunity cost of selling a truck is selling:

Dent ‘n’ Scratch Used Cars and Trucks employs 3 salesmen. Data for their sales last month are shown in this table: Based on last month’s data, Joe’s opportunity cost of selling a truck is selling:
A.4 cars.
B.1/3 of a car.
C.9 cars.
D.1 car.
正确答案：1 car.