1. [Its / it’s] better to give than to receive.
2. We always throw a big party on my [mother’s / mothers / mothers’] birthday.
3. [They’re / There / Their] are three [pieces / piece’s] of pie left.
4. [Jims / Jims’ / Jim’s] teacher said that [your / you’re] wrong.
5. She could never finish one of [Dickens / Dickens’ / Dickens’s / Dicken’s] novels.
6. The dog growled and bared [its / it’s] fangs.
7. The [boys / boy’s] father said the baseball was his [son’s / sons], but we knew it was [ours / our’s].
8. The [Simpsons’ / Simpsons / Simpson’s] television is a central part of their lives.
9. The [skies / sky’s] the limit.
10. After three [days / day’s / days’] worth of work, they completed the project.

Explanations

1. It’s better to give than to receive.
   [ “It’s” is a contraction for “it is.” ]
   
2. We always throw a big party on my mother’s birthday.
   [The apostrophe indicates possession: “the birthday of my mother.” “Mother” is singular, so an apostrophe and an “s”are added.]
   
3. There are three pieces of pie left.
   [In this case, “there” is an expletive — it doesn’t indicate possession (their) or a contraction (they are). “Pieces” is simply the plural of “piece” and does not require an apostrophe.
   
4. Jim’s teacher said that you’re wrong.
   [“Jim’s teacher” is another way of saying “the teacher of Jim.” “Jim” is singular, so the possessive is made by adding an apostrophe and “s.”]
   
5. She could never finish one of Dickens’s novels.
   [“Dickens” is singular; therefore, an apostrophe and “s”are added to make it possessive.]
   
6. The dog growled and bared its fangs.
   [Here, “its” is possessive: “the fangs of the dog.” Possessive pronouns do not include apostrophes.]
   
7. The boy’s father said the baseball was his son’s, but we knew it was ours.
   [Both “boy’s” and “son’s” are singular possessive forms (adding apostrophe and ”s” to the singular noun). “Ours” is a possessive pronoun and thus does not include an apostrophe.]
   
8. The Simpsons’ television is a central part of their lives.
   [“Simpsons” is plural. Therefore an apostrophe is added after the “s” that’s already there.]
   
9. The sky’s the limit.
   [“Sky’s” is a contracted version of “sky is.”]
   
10. After three days’ worth of work, they completed the project.
    [The rules for this type of expression follow those for forming possessives. “Days” is plural, so an apostrophe follows the existing “s.”]