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The teacher’s book (one teacher)
The students’ essays (several students)
Use ’s after plural nouns that don’t end in s:
people’s rights; children’s toys
Use the apostrophe alone after plural nouns that end in s:
the neighbours’ house
Use an apostrophe in time constructions such as:
eight weeks’ time; two weeks’ leave
Do not use the apostrophe in possessive pronouns: hers, its, yours, etc.
Do not use the apostrophe in year dates: the 1960s, the 1990s
As a general rule, do use ’s after names that end with an s or z sound:
Marx’s; Charles’s; Jones’s; Davis’s
If it is awkward to pronounce, then leave off the final s.
Classical names don’t use the final s: