A demand curve for a public good is determined by

A) summing vertically the individual demand curves for the public good.
B) summing horizontally the individual demand curves for the public good.
C) combining the amounts of the public good that the individual members of society demand at each price.
D) multiplying the per-unit cost of the public good by the quantity made available.

The demand curve for a public good is determined by summing vertically the individual demand curves for the public good. This is because public goods are non-excludable and non-rivalrous, meaning that one person's consumption does not reduce the amount available for others, and it's not possible to exclude others from using the good. Therefore, the total willingness to pay at each price level is the sum of the individual willingness to pay, which is represented by vertical summation.