The Construction of a Market Demand Curve for a Private

The construction of a market demand curve for a private good differs from that for a public good in that

A) there is no difference; in both cases the demand curve is determined by adding up the price each consumer is willing to pay for each quantity of the good.
B) there is no difference; in both cases the demand curve is determined by adding up the quantities demanded by each consumer at each price.
C) the market demand curve for a private good is determined by adding up the quantities demanded by each consumer at each price, but the market demand curve for a public good is determined by adding up the price each consumer is willing to pay for each quantity of the good.
D) the market demand curve for a private good is determined by adding up the price each consumer is willing to pay for each quantity of the good, but the market demand curve for a public good is determined by adding up the quantities demanded by each consumer at each price.