Which of the examples below demonstrates the principle economists call the "law of diminishing returns"?

a) As a baker adds new ovens and new workers, eventually it will be able to to produce more bread than consumers want.

b)As more and more gasoline stations are built in a city, the average profit captured by gasoline station will fall

c)An office manager can produce the same number of copies in an hour with a few workers and many copy machines as with many workers and a few copy machines.

d) As a farmer increases the number of workers picking apples in an orchard, eventually the orchard becomes overcrowded and the workers get in each other's way, reducing productivity.