Answer:
C. Because the couple is divorced, the IRS must apportion the deficiency between Mr. and Mrs. Pitt based on their relative contribution to their 2015 taxable income.
Step-by-step explanation:
Because Mr and Mrs Pitt filed for a joint tax return in 2017 and got divorced in 2018 and IRS audited their tax return and found that they both underpaid their tax, the IRS must apportion the deficiency 50-50 between both of them based on their separate returns.