PEOPLE to take care of them, because of illness that they have had for a long time".E.g. She had been a delicate CHILD and her parents had TREATED her as an invalid.From the meaning and example that are given above, 'invalid' is the correct answer. Let's look at the meanings of other words:Athlete- a person who competes in sports.Activist- a person who WORKS to achieve political or social change, especially as a member of an organization with particular aims.Petitioner- a person who organizes or signs a PETITION.