GMAT Critical Reasoning (CR) | Re: Urban air contains more sulfur dioxide than does rural air,

I have read several explanations for this problem across various forums and am not satisfied with any of the answers. So, I decided to think this problem thoroughly and here is my explanation:
Facts:
Urban air SO2 > Rural air SO2
Urban plant growth < Rural plant growth

Is there are relation between SO2 and plant growth?

Experiment is conducted to filter out SO2. "Assuming" we have only one factor that affects the plant growth and that is SO2, then the result of the experiment
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