A regressive tax is the opposite of a progressive tax and is applied uniformly regardless of the taxpayer, so it ends up taking a larger percentage from low income tax payers than from high income tax payers.
D is the correct answer because eventually the regressive tax uniformity tends to be a disadvantage for the lower income taxpayer who has to pay the same amount of taxes with much less income than a high income taxpayer.
When it comes to income tax, the United States has a progressive taxation system which mean that the taxpayers who earn a higher income will pay more, but there are some inconsistencies to the system like state sales taxes, user fees and even property taxes to some extend. These inconsistencies are considered a form of regressive taxes, like levies imposed which ultimately affect low income taxpayers.