Which of the Following Describes the Difference Between the Market

Which of the following describes the difference between the market demand curve for a private good and the demand curve for a public good?

A) The market demand curve for a private good is derived by adding vertically the quantities that consumers demand at each price.The demand curve for a public good is derived by adding horizontally the quantities that consumers demand at each price.
B) The market demand curve for a private good is derived by adding horizontally the quantity of the good demanded at each price by each consumer.The demand curve for a public good is derived by adding up the price each consumer is willing to pay for each quantity of the good.
C) The market demand curve for a private good will always is downward sloping.The demand curve for a public good will always is upward sloping.
D) The market demand curve is drawn holding everything other than the price of the good constant; the demand curve for a public good is drawn by allowing all variables that affect demand to change.