Final answer:
Rosa would pay the smallest percentage of her income in taxes under a regressive tax system.
Step-by-step explanation:
Under a regressive tax system, the percentage of income paid in taxes decreases as income increases. In this case, since Nicole earns the least, Michelle earns in the middle, and Rosa earns the most, Rosa would pay the smallest percentage of her income in taxes. Therefore, the answer is C. Rosa.
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