The appeal to ethos is an argument that is based on the credibility or trustworthiness of the speaker or writer.
Out of the options given, the appeal to ethos is best represented by option C: "We all want the elderly to receive quality care." This statement suggests that the speaker is trustworthy and has the best interests of the elderly in mind. It also appeals to the shared values of the audience, implying that caring for the elderly is a universal concern.