Which of the Following Examples Best Describes the Concept of Diminishing

Which of the following examples best describes the concept of diminishing marginal benefit?

A) If the weather gets cold, the demand for ice cream will fall.
B) With each additional pen Jill buys, her willingness to pay for another pen decreases.
C) Each additional unit of ice cream that John consumes gives him more and more satisfaction.
D) If a seller of notebooks in a perfectly competitive market charges above the market price, his profit decreases.