While preparing Margaret’s Form 1040, John discovers an error on her prior-year tax return, which Margaret prepared herself, in which Margaret’s adjusted gross income (AGI) was understated by $10,000, roughly 10% of AGI. What is John’s responsibility concerning the error?

a. Do nothing, since the understatement was less than 25% of Margaret’s AGI.

b. Correct the error on the current-year return, without Margaret’s knowledge.

c. Request that Margaret correct the error, and notify the IRS if she doesn’t.

d. Request that Margaret correct the error, and consider withdrawing from the engagement if she doesn’t.