<em>Answer: I think it would be energy from Earth's gravitational force.</em><em> </em>
Explanation:
- B.) Egyptians was first ruled by the Greeks and then the Romans
The Mound Builders used metal tools, and were probably metal builders. Based on that information I would say the answer is B.Copper, because copper is a metal.
-Pointed arches are better approximations of catenary curves that represent the line of compressive force acting in any arch, and thus they exert less outward or overturning thrust. They also present considerable design flexibility, as one can vary to some extent the angle of the arch.
-Rib vaulting builders found that they could lighten the webbing, thereby reducing the material weight of the groin. Reducing the weight of the stone, would allow them to also build to greater building heights.
-Flying Butresses were created to strengthen the upper sections of the skeleton frame because the height of these buildings left them needing reinforcement.