Answer:
The correct answer is letter "D": Cindy can claim Mark as a dependent and she can file as head of household.
Step-by-step explanation:
Dependents are people taxpayers entitles as such to claim exemptions in a tax return. Dependents can be "qualifying child" or "qualifying relative". In the case of qualifying relatives, the dependent must meet the Dependent Taxpayer Test, Joint Return Test, Citizen or Resident Test, Member of Household or Relationship Test, Gross Income Test, and Support Test. The dependent exemption for 2017 is $4,050. Thus, Mark can be considered as Cindy's dependent because they lived in the same household during the same year with nobody else even if he is not working and he is not disabled.
For taxing purposes, being head of household implies paying more than half of the housing expenses, not being married for the past year, and having a qualifying dependent. Then, as Cindy provided all the support of her household, has not married recently, and has Mark as her dependent, she can be considered the head of the household.