During the Course of an Audit, a CPA Discovers an Error

During the course of an audit, a CPA discovers an error in a prior return. According to the Statements on Standards for Tax Services, the CPA should

A) correct the error in the current year's tax return.
B) ask the client for permission to disclose the error to the IRS.
C) inform the IRS of the error, regardless of whether the client grants permission.
D) withdraw from the engagement.