Kyle and Elena Smith contributed to the support of their two children, Alexandra and Matthew, and Elena's divorced father, Nick. For 2016, Alexandra, a 22-year-old full-time college student, earned $1,700 from a part-time job. Matthew, a 27-year-old full-time graduate student, earned $23,000 from his job as a teaching assistant. Nick received $12,000 in capital gains income and $7,000 in nontaxable Social Security benefits. Alexandra, Matthew, and Nick are U.S. citizens and were over one-half supported by Kyle and Elena. How many exemptions can Kyle and Elena claim on their 2016 joint income tax return?
a. 2
b. 3
c. 4
d. 5