Answer the Question on the Basis of the Following Information

question 20

Multiple Choice

Answer the question on the basis of the following information for a public good.P_a and P_b are the prices that individuals A and B are willing to pay for the last unit of a public good,rather than do without it.These people are the only two members of society. $\begin{array}{c}\begin{array}{c}\underline{\text {Q }}\\1 \\2 \\3 \\4 \\5\end{array}\begin{array}{c}\underline{\mathrm{Pa}_{\mathrm{a}} }\\\$ \\2\\1\\0\\0\end{array}\begin{array}{c}\underline{\mathrm{Pa}_{\mathrm{b}} }\\\$ 5 \\4 \\3 \\2 \\1\end{array}\end{array}$
Refer to the data.If the marginal cost of producing this good at the optimal quantity is $4,the optimal quantity must be:

• A) 1 unit.
• B) 2 units.
• C) 3 units.
• D) 4 units.