Global ecological problems reduce to the problem of balancing supply and demand.
Evidence
Global ecological problems reduce to the problem of balancing supply and demand.
Supply is strictly confined by the earth's limitations.
Demand, however, is essentially unlimited, as there are no limits on the potential demands made by humans.
The natural tendency for there to be an imbalance between demand and sustainable supply is the source of these global problems.
Conclusion
Any solutions require reducing current human demand.
Evaluate
When an author is concluding that we MUST take a certain course of action (to solve a problem / achieve a goal), the most likely direction the correct answer is headed is considering whether there are Alternative Options.
When an author says, , they are automatically assuming: 1. Y is a way to get X 2. there are no other ways to get X
But correct answers almost always deal with #2, the possibility of Alternative options.
If we're trying to balance demand and sustainable supply, we could potentially raise/lower demand to meet supply, or we could raise/lower supply to meet demand (or both).
The author thinks our only option is lowering demand, so she's assuming - we can't correct an imbalance by increasing demand - we can't correct an imbalance by increasing / decreasing supply