English Plus+
Grammar Slammer's Apostrophes Showing Possession
This site discusses the correct and incorrect usage of apostrophes to show possession and examples are provided. Note that links are provided at the bottom of the page for other specific uses of the apostrophe.
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Sandhills Community College: The Apostrophe
A valuable resource for learning about the uses of the apostrophe in English punctuation, including apostrophes with possessive nouns as well as contractions. Provides examples.