GMAT Critical Reasoning (CR) | Ten years ago, the total share of federal, state, and local taxes

This question can convincingly be solving using POE. Option C doesn't jump out to me as correct answer choice. Option C states that Tax payers are paying lesser percentage from their income. But the issue is, it could be possible that an average tax payer's income has increased, and now even a smaller percentage equates to the same percentage contribution as before. Hence there isn't any change in the total money contributed via taxes. But still the total %tage contribution to GNP is lower. This
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