Which of the following is an argument, on its own, for de-growth as necessary for environmental sustainability?

a. The ecological footprint is currently unsustainable, and it would be impossible to

reduce the ecological footprint without reducing the size of the economy.

b. Marginal returns to human well-being (marginal utility) diminish as the economy growth, and marginal ecological harm (marginal disutility) increases. Thus, economic growth should stop when the economy reaches the size where marginal utility equals marginal disutility.

c. It is difficult, but possible, to decouple the ecological footprint from growth.

d. Technological innovations might allow the current economy to be powered by external energy sources.