The correct answer is: A. Contract curve in the Marshall Edgeworth input box.
The contract curve is a locus of points in the Edgeworth box representing all possible Pareto efficient allocations of two goods between two consumers. The production possibility curve is a graph showing the maximum amounts of two goods that can be produced with a given amount of resources. The production possibility curve is based on the contract curve in the Marshall Edgeworth input box because the contract curve shows all the possible combinations of goods that can be produced with a given amount of resources, and the production possibility curve shows the maximum amounts of goods that can be produced with a given amount of resources.
The contract curve in the Marshall Edgeworth output box is not a valid option because it is not a locus of points representing all possible Pareto efficient allocations of two goods between two consumers. The social welfare function is not a valid option because it is a function that represents the preferences of society as a whole, and the production possibility curve is not a function. The price-ratio line is not a valid option because it is a line that shows the relative prices of two goods, and the production possibility curve is not a line.