The Table Above Shows a Nation's Production Possibilities Frontier

Multiple Choice

$\begin{array} { c c c } \hline \text { Possibility } & \text { Robots } & \text { Pizza } \\\hline A & 0 & 40 \\B & 1 & 39 \\C & 2 & 37 \\D & 3 & 34 \\E & 4 & 30 \\F & 5 & 20 \\G & 6 & 0 \\\hline\end{array}$
The table above shows a nation's production possibilities frontier. The opportunity cost of a robot between combination D and E is

A) 30 pizzas.
B) 4 pizzas.
C) 1/4 of a pizza.
D) 34 pizzas.
E) undefined because neither point is production efficient.