answer: #Person1# tells #Person2# December the seventeenth is Tom's birthday, and they plan to invite their friends to celebrate.
documents: #Person1#: What's the date today?
  #Person2#: December the fifteenth. The day after tomorrow is little Tom's birthday.
  #Person1#: Right. What present should we give him this time? By the way, how old is he?
  #Person2#: Thirteen today and tomorrow. Fourteen the day after tomorrow.
  #Person1#: How time flies! He's a big boy now.
  #Person2#: And don't forget Mary, Tom's twin sister. It's her birthday, too.
  #Person1#: OK. Let's invite all their little friends to come and celebrate.