Table 13 Shows the Hypothetical Trade-Off Between Different Combinations of Brushes

Table 1.3 shows the hypothetical trade-off between different combinations of brushes and combs that might be produced in a year with the limited capacity for Country X,ceteris paribus. Table 1.3
Production Possibilities for Brushes and Combs
$$\begin{array} { | l | c | c | r | r | } \hline \text { Combination } & \begin{array} { c } \text { Number of } \\\text { combs }\end{array} & \begin{array} { c } \text { Opportunity } \\\text { Cost(Foregone } \\\text { brushes) }\end{array} & \begin{array} { c } \text { Number of } \\\text { brushes }\end{array} & \begin{array} { c } \text { Opportunity Cost } \\\text { (Foregone combs) }\end{array} \\\hline \mathrm { J } & 4 & & 0& \text { NA } \\\hline \mathrm { K } & 3 & & 10 & \\\hline \mathrm { L } & 2 & & 17 & \\\hline\mathrm { M} & 1 & & 21 & \\\hline \mathrm { N } & 0 & \text { NA } & 23 & \\\hline\end{array}$$ On the basis of Table 1.3,in the production range of 21 to 23 brushes the opportunity cost of producing one more comb in terms of brushes is

A) 1/21.
B) 21/23.
C) 1/2.
D) 4.