Why is D correct? Why is B incorrect?

@Ryan-Mahabir, (B) is incorrect because Passage A argues that flax taxes do work well in the real world and addresses any misconceptions to the contrary. (D) is correct because Passage A concludes that opportunities to avoid taxes for high-income earners are enormous under a progressive tax regime, resulting in high-income earners paying about the same amount of tax under a flat-tax regime (lines 22-29), thus implying that opportunities to avoid tax are more limited under a flat-tax. Passage B does not address this conclusion.