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D is corrent. The requirement is to determine Robert’s filing status and the number of exemptions that he should claim. Although the social security of $9,700 is excluded from gross income, Robert’s father does not qualify as Robert’s dependent because his father’s gross income (interest income of $4,100) was not less than $3,800. Since his father does not qualify as his dependent, Robert does not qualify for head-of-household filing status. Thus, Robert will file as single with one exemption.
A is incorrect because his father’s gross income prevents him from being a qualifying relative. 
B is incorrect because his father’s gross income prevents him from being a qualifying relative.
C is incorrect because to be a head of household, a taxpayer must maintain a household for a dependent relative.