Identify a characteristic of the houses designed by Adolf Loos.
1) The interiors of these houses had flat but beautifully decorated false ceilings to avoid unevenness.
2) The exterior of the houses designed by Loos was loaded with complex designs and ornament.
3) The materials used in the construction of these houses were usually concrete, steel, and glass.
4) The exteriors and the interiors of the houses designed by Loos had no conventional ornament.