theirs       
pronoun uk/ðeəz/ us/ðerz/
A2 他们的,她们的,它们的(所有物)
the one(s) belonging to or connected with them
  Which children are theirs? 那些孩子是他们的? 
 I think she's a relation of theirs. 我想她是他们的亲戚。 
 Theirs is that little house with the big tree outside. 他们的家是那栋屋外有棵大树的小屋。 
 - More examples
 - The Taylors had the same suitcase as us, and we accidentally picked up theirs.
 - I'd love a house like theirs - I'm so envious!
 - Our school uniform is much nicer than theirs, don't you think?
 - The neighbours have erected a huge fence between our house and theirs.
 - Your name was spelled correctly in the copy we gave to the printers, so the mistake was definitely theirs, not ours.