Will and Brenda live in New York City are both aged 66 and always file a joint tax return. During the current year, they provide all the support for their son who is 20, has no income, and is a part-time college student. Their daughter, age 22 and a full-time student at Columbia University, has $4,800 as income. Which of the following is true of Will and Brenda's tax return? 

a). Only their son is a dependent. 

b). Only their daughter is a dependent. 

c). Neither their son nor their daughter is a dependent. 

d). Both their son and their daughter are dependents.