Is it ture or false the more you have of a substance , the greater it's density is

Why have the aztec ruins in mexico city not been dug up?

The controlled use of fire by hominids: (a) limited the expansion of hominids into certain environments, such as dry grasslands. (b) decreased the amount of food energy available in the hominid diet. (c) contributed to geographical expansion and food production techniques in positive ways. (d) has been shown to contribute little to the digestive process of hominids.

Where is sub-saharan africa located?