A report on the likely effects of current levels of air pollution on forest growth in North America concluded that, since nitrogen is a necessary nutrient for optimal plant growth, the nitrogen deposited on forest soil as a result of air pollution probably benefits eastern forests.
Your task
Break the argument into its conclusion and evidence, then do exactly what the question stem asks with that structure.
Common trap
Answers that sound relevant to the topic but don't connect to the argument's actual reasoning.
Winning move
Predict what a right answer must do, then test each choice against the conclusion-evidence gap.