The Marginal (Dollar)cost of an Additional Plate of Food to a Patron

The marginal (dollar) cost of an additional plate of food to a patron at an "All-You-Can-Eat" restaurant is:

A) equal to the price paid for the meal divided by the number of plates of food consumed.
B) equal for all plates of food consumed during the meal.
C) equal to zero.
D) equal to the price paid for the meal (since there is no such thing as a free lunch) .