In Up for Debate: "Should the Federal Income Tax Be

In Up for Debate: "Should the Federal Income Tax Be Changed to a Flat Tax?", it is argued that

A) a flat tax on income is a regressive tax.
B) the current system works well with its exemptions and brackets and should be retained.
C) with all of the shelters and exemptions, the federal income tax has lost its progressive nature.
D) a flat tax is always good because it relieves the tax burden on low income earners.