Dent 'N' Scratch Used Cars and Trucks Employs 3 Salesmen

Dent 'n' Scratch Used Cars and Trucks employs 3 salesmen.Data for their sales last month are shown in this table: $$\begin{array} { | l | l | l | } \hline & \text { Cars Sold } & \text { Trucks Sold } \\\hline \text { Larry } & 10 & 5 \\\hline \text { Joe } & 9 & 9 \\\hline \text { Ralph } & 3 & 12 \\\hline\end{array}$$
For Joe,the opportunity cost of selling a truck is:

A) 9 fewer cars sold.
B) 1 fewer cars sold.
C) 4 fewer cars sold.
D) 1/3 car not sold.