Karl's client is a married woman who wants to claim the earned income credit using head of household filing status. Which of the following should Karl do to perform the appropriate due diligence with respect to his client claiming the credit?\ A) Confirm that the client's 2023 AGI was less than $20,000\ B) Ensure the client did not live with her spouse at any time during the last six months of the year\ C) Obtain a copy of the client's marriage license\ D) Ensure the client had no investment income