Choice "D" is correct. With respect to the penalty for aiding and abetting an understatement of tax liability on a tax return, the burden of proof shifts to the IRS from the taxpayer. Unless the law expressly states otherwise, the taxpayer has the burden of proof to establish by the preponderance of the evidence that the law and the evidence do not support the position of the IRS. With respect to any criminal action, the government has the burden of proof to establish by evidence beyond a reasonable doubt that the taxpayer is guilty of the charges. Note that these burdens of proof are different; criminal (beyond a reasonable doubt) is considerably higher than civil (preponderance of the evidence).Choice "b" is incorrect. The penalty for aiding and abetting an understatement of tax liability on a tax return applies to any person, not just to tax return preparers.Choice "a" is incorrect. The penalty for aiding and abetting an understatement of tax liability on a tax return applies whether or not the understatement is with the knowledge or consent of the person authorized or required to file the return.Choice "c" is incorrect. The civil penalty for aiding and abetting an understatement of tax liability on a tax return is $1,000 for all taxpayers except corporations and $10,000 for corporations, not $10,000 and $100,000.