answer: #Person1# and #Person2# are talking about a book that introduces interesting buildings from all over the world, including pyramids, the pentagon, the cylindrical office building, the world's largest sports stadium, etc.
documents: #Person1#: That looks like an interesting book.
  #Person2#: It is. It's got pictures of interesting building from all over the world, with brief descriptions of how they were build, their purpose, and so on.
  #Person1#: There are the pyramids. It's easy to see how they got that name! they don't have smooth sides though.
  #Person2#: They don't now, but most of them did originally. There's picture of the pentagon in the united states. It's very distinctive with its five sides.
  #Person1#: Look at that cylindrical office building. I'Ve never been seen one that shape before.
  #Person2#: Yes. Usually only TV towers are cylindrical in shape.
  #Person1#: TV towers are usually thicker at the bottom than at the top. They're not perfectly cylindrical.
  #Person2#: This is the world's largest sports stadium. It's a massive oval.
  #Person1#: What sports do they play there?
  #Person2#: It says here that it's m mainly used for big football matches and athletics meetings.
  #Person1#: Is that building a perfect cube?
  #Person2#: According to the book, it is. I'Ve never seen a building that is a perfect cube. Look at the building. From the air, it looks like a square with a semi-circle attached to each of its four sides. What
  #Person1#: Is says here that it's a war memorial. Now, there's a distinctive structure-the stomium in Brussels. See? It consists of several connected by cylinders. I believe you can go up and down inside it.