Which of the following individuals must file a tax return in 2018?
a. Carolyn is single and age 66. She receives $2,000 of interest income, $3,000 of dividend income, and $6,000 in Social Security benefits.
b. Tim is single, age 18, and a full-time student. He is a dependent of his parents. Tim earned $2,000 from a part-time job and $400 in interest income.
c. Justin is single, age 25, and a full-time graduate student. He earned $11,750 from a part-time job.