Which of the following acts by a CPA will not result in a CPA's incurring an IRS penalty?

Which of the following acts by a CPA will not result in a CPA’s incurring an IRS penalty? 2. A.Understating a client’s tax liability as a result of an error in calculation. B.Failing, without reasonable cause, to provide the client with a copy of an income tax return. C.Failing, without reasonable cause, to sign a client’s tax return as preparer. D.Negotiating a client’s tax refund check when the CPA prepared the tax return.