Concept:Some nouns borrowed from Greek or Latin keep their original plural forms. "Criteria" is the plural of "criterion", while the other options are singular.Explanation:- "Criteria" is the plural form of "criterion". A criterion is a standard for judgment.- "Analysis" is singular; its plural is "analyses". It means a detailed examination.- "Crisis" is singular; its plural is "crises". It means a time of intense difficulty.- "Index" is singular; its plural can be "indices" or "indexes". It is a list of topics or names.- Therefore, among the four options, only "criteria" is already in its plural form.Answer:D. Criteria