All of the following taxpayers were unmarried at the end of the year. Which one must file a 2021 federal income tax return?

Damien (48), single, gross income $11,750.

Titania (72), single, gross income $13,330, all from pensions.

Myrna (24), head of household, gross income $18,950.

Misty (66), head of household, gross income $19,900.