I JUST NEED AN QUICK ANSWER THANK YOU! Which of the following is an example of the law of diminishing marginal returns?

a. Holding capital constant, when the amount of labor increases from 5 to 6, output increases from 25 to 35. Then when labor increases from 6 to 7, output increases from 35 to 38.

b. Holding capital constant, when the amount of labor increases from 7 to 8, output increases from 36 to 42. Then when labor increases from 8 to 9, output increases from 42 to 55.

c. When labor increases by 20 percent and capital decreases by 15 percent, output remains constant.

d. When capital and labor both increase by 20 percent, output increases by only 15 percent.