2.1 Nouns, Pronouns, and Agreement
Make Nouns Possessive
(1) A charity auction and a supporters’ generous contribution paid for a new wing of the childrens’ hospital.
(2) The auction’s most expensive item was tickets to the president’s inauguration party.
Sentence (2) is correct. Auction and president are singular nouns, so adding an apostrophe and -s is correct. In sentence (1), a supporter is singular, so the possessive should be supporter’s. Also, children is a plural noun that doesn’t end in -s, so the possessive should be children’s.