When Creating Demand Curves for a Good Where One Group

When creating demand curves for a good where one group gets the good for free and another group must pay the market price, we must

A) add the quantity demanded for each group at each price.
B) add the price paid at each quantity.
C) take an average of the quantity demanded at each price.
D) add the amount that the first group wants when its free to them to the quantity demanded for the second at each price.