Choice "C" is correct. The negligence penalty with respect to understatement of tax is an accuracy-based penalty for negligence or for disregard of tax rules and regulations.
Choice "b" is incorrect. The negligence penalty with respect to understatement of tax is computed as 20%, not 25%, of the understatement of tax.
Choice "a" is incorrect. The negligence penalty with respect to understatement of tax defines "disregard" as any careless, reckless, or intentional, not unintentional, disregard of tax rules and regulations.
Choice "d" is incorrect. The negligence penalty with respect to understatement of tax is not imposed in conjunction with the penalty for substantial underpayment of tax and the penalty for a substantial valuation misstatement. If the negligence penalty with respect to understatement of tax is imposed, the other two penalties cannot also be imposed.