Which Best Illustrates the Concept of Diminishing Marginal Utility

Which best illustrates the concept of diminishing marginal utility?

A) Gladys is hungry and the first piece of pizza she eats tastes wonderful! The fifth piece of pizza she eats makes her sick.
B) Thomas likes tomatoes more than Janice, and thus gets more utility from tomatoes than Janice does.
C) High Fly is a new low-cost airline. Initially, it is very expensive for High Fly to offer flights to customers because of the high start-up costs, but after covering fixed costs, the additional cost of adding one more consumer falls significantly.
D) Sarah likes hamburgers, but the price she is willing to pay for them is low compared with another good she also likes.