John and Mary Have Two Children, Anna, Age 16, and Tammy

John and Mary have two children, Anna, age 16, and Tammy, age 21. Anna works after school and earned $4,000 in 2017. Tammy works 30 hours per week and is a part-time student at the local community college. She earned $8,400 in 2017. John's mother also lives with them; she receives $7,800 in Social Security and $2,000 in interest income from some bonds. John and Mary provide over $10,000 towards her support. How many dependency exemptions may John and Mary claim on their joint tax return?

A) 1
B) 2
C) 3
D) 5