The materials in the sculpture--wood, steel, aluminum, and plastic--can be reflected upon as a part of our past (the importance of wood in agrarian growth), our present (the utilization of steel and aluminum in various local industries), and our future (the expanding use of plastic in high-technology fields).
(The materials in the sculpture; can be reflected; as a part of our past)
The materials in the sculpture
can be reflected
as a part of our past