Choose the correct options

1. These are
   [their|theirs]
   books.
2. Whose bag is it? — It is
   [her|hers].
3. Look at
   [our|ours]
   new car. It's fast.
4. This is Carol. It is
   [her|hers]
   sister.
5. Don't take this pen. It's not
   [your|yours].
6. This is your bike, and that is
   [my|mine].
7. Our student books are new, and
   [their|theirs]
   are old.