Oque é constatação?preciso pra aula de geografia

The large connected urbane area from boston to washington, d.c. is often referred to as

Acivilization exists for several hundred yeaars, developing its own language. such a civilization probably has been: a. farming corn b. suffering from a lack of contact with the outside world. c. isolated by mountains or some other physical barriers. d. starving from lack of trade.

What is the border between layers a through f and layer g called?