An apostrophe replaces a missing letter (or letters) or indicates "possession" (belonging to).

For example:

Missing letters:

I cannot (can't) remember my name!

He is (he's) a silly billy.

We are (we're) going to the beach tomorrow.

Possession: (if we are talking about one person or one thing's possession the apostrophe goes before the 's')

The Storyteller's hat was yellow.

Annnabelle's pearls were plum-coloured.

The bird's feathers were red and black with white spots.

(if we are talking about more than one person or thing's possession then the apostrophe comes AFTER the 's')

The cows' calves were leaping around the field.

The boys' football went over the fence.

The dogs' baskets were in the corner.

HOWEVER (and this is a great big HOWEVER)

...if you are using a "pronoun" replacement for the owner of the possession (his, her, our, your, their) then because the pronoun you are using already shows possession you do NOT use an apostrophe at all!!!

Therefore:

This book is yours.

Yours is bigger than ours.

His hair was longer than hers.

1. The Storyteller's nightmare!
   
   The Storyteller was out for a walk with his friend Annabelle Angermanagement (think we can guess why she was called that - and haven't we all just been down that road? Take a deep breath now!). They came to a field full of cows.
   
   The ________warm breath misted the air and the birds in the tree sang merrily.

   1.   ?    cows
   2.   ?    cow's
   3.   ?    cows'

2. At the top of the tree was a big purple bird and ____ beak was bright, bright pink.
   
   Annabelle Angermanagement stamped her foot. Oh dear, she was getting cross!

   1.   ?    its
   2.   ?    it's
   3.   ?    its'

3. Annabelle shook her head violently and the cows all shook _______.
   
   The Storyteller stepped back and looked carefully at the big purple bird with the pink beak.

   1.   ?    theirs'
   2.   ?    theirs
   3.   ?    their's

4. "Why are you so angry at the sight of the big purple bird with the pink beak?" asked the Storyteller of Annabelle.
   
   Annabelle stomped a bit more and shouted at the top of her voice:
   
   "I ________ COPE WITH BIG PURPLE BIRDS WITH PINK BEAKS!!!! YOU KNOW THAT, STORYTELLER, EVER SINCE MY RUN IN WITH PROSPER PROUDFOOT LAST YEAR!!!!"
   
   

   1.   ?    can't
   2.   ?    cant
   3.   ?    can not

5. The Storyteller sat down.
   
   "I remember ___________ pet parrot pinched your plum pearls at the Village Fete," he puzzled, "but I am not sure why that has affected your view on big purple birds with pink beaks. That parrot was red and black with white spots if I remember rightly!"

   1.   ?    Prospers
   2.   ?    Prospers'
   3.   ?    Prosper's

6. "Oh, are you sure?" questioned Annabelle more calmly. "When I dream about it ____ got purple feathers and a pink beak!"
   
   She sat down beside the Storyteller.

   1.   ?    it's
   2.   ?    its
   3.   ?    its'

7. They sat quietly for a while and pondered the situation.
   
   In the meantime the big purple bird with the pink beak spotted them sitting there and decided to swoop.
   
   Well, it swooped this way, it swooped that way, then it swooped back again.
   
   The Storyteller and Annabelle lay flat on the ground.
   
   "MIND YOUR HEAD!!!" screamed Annabelle.
   
   "I AM, I AM, JUST YOU MIND ________!!!" screeched the Storyteller.

   1.   ?    YOUR'S
   2.   ?    YOURS'
   3.   ?    YOURS

8. All that screeching scared the big purple bird with the pink beak and it flew away over the tree tops.
   
   As it went it took off its big purple body suit and its pink beak. It dropped them to the ground where a very surprised rabbit found them a week later and spent the next day jumping out at its ________ and relations until they got so fed up they sewed up all the holes so that the poor rabbit was stuck in a hot sweaty bodysuit for quite the next three and a half weeks!

   1.   ?    friend's
   2.   ?    friends
   3.   ?    friends'

9. The black and red parrot with the white spots (for yes, it was he), flew away over the _______ topmost branches, jangling his rather smart row of plum pearls as he went.

   1.   ?    trees
   2.   ?    tree's
   3.   ?    trees'

10. The Storyteller and Annabelle were, of course, none the wiser. But, I have to say, Annabelle's nightmares continued to be of a big purple bird with a pink beak. _______ to say why?

    1.   ?    whose
    2.   ?    who's
    3.   ?    whos