Concept:Many English words borrowed from Greek or Latin form plurals by changing the ending instead of adding -s. For example, words ending in -is often change to -es, and words ending in -on change to -a.
Explanation:The question asks for the word that is already in its plural form.
- 'Index' is singular. Its plural forms are 'indexes' or 'indices'.
- 'Analysis' is singular. Its plural is 'analyses'.
- 'Crisis' is singular. Its plural is 'crises'.
- 'Criteria' is plural. It is the plural of 'criterion'.
Among the given options, only 'criteria' is already a plural word.
Answer:D. Criteria