Well, the correct answer about Joseph Paxton's Crystal Palace is that it was unconventional because the iron support structure was visible. Since it was made from iron and glass, of course that the structure could be seen.
The correct answer is that the iron support structure was visible
When you build something, the structural points such as pillars are usually not easily discernible to the untrained eye because they fit right there with the remaining walls and things like plaster or bricks. However, his Palace was built out of Glass so the iron supporting structures could easily be seen and it looked great.
