Which of the Following Statements Is True of the Concept

Which of the following statements is true of the concept of willingness to pay?

A) The willingness to pay is the lowest price that a buyer is willing to pay for an extra unit of a commodity.
B) The willingness to pay for a commodity increases exponentially as the consumption of the commodity increases.
C) The willingness to pay for a commodity increases linearly as the consumption of the commodity increases.
D) If a consumer is consuming 10 units of a commodity and she is ready to pay $2 for the eleventh unit, her willingness to pay for the eleventh unit is $2.