Nouns can be singular (as in Lesson 16) or be plural in form. Plural means two or more. Plurals are formed by adding s, es, changing y to i and adding es, and with changes in spelling as in man becoming men. Examples: car, cars; fox, foxes; baby, babies; man, men.
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from Daily Grammar Lessons Blog http://dailygrammarlessons.blogspot.com/2018/09/lesson-17-parts-of-speech-nouns.html