While this is a good summary of the neoclassical view, this is not the main point of the passage as a whole. The main point of the passage is to show that the steady-state model is an alternative to the neoclassical model, but (A) doesn’t say anything about what the steady-state model is or why it could be an alternative to neoclassical economics.

Like (A), this is a good summary of neoclassical economics, but this misses the overall main point. The main point of the passage is to show that the steady-state model is an alternative to the traditional neoclassical model, but (B) doesn’t say anything about what the steady-state model is or why it’s a good alternative to neoclassical economics.

This is not an accurate summary of the steady-state view. It’s the neoclassical economists who warn about economic stagnation when growth is limited, but in response, the steady-state economists say that there are alternatives to growth that can still satisfy human desires. Also, conservation is just one possible alternative to growth, not the definitive alternative to growth.

(D) captures the author’s point that the steady-state model is an alternative to the neoclassical model, and why. In contrast with the neoclassical economists, the steady-state economists think that resource availability limits the ideal size of the economy, and that conservation is one alternative to growth to make sure that the economy still satisfies human desires.

This is not supported by the passage. Steady-state economists don’t believe in unlimited growth, so they don’t want unimpeded increase in exchange value.