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

What are the answers for the following questions?

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.

Which statements describe cultural influences? florida is bordered by water on three sides. french is spoken in parts of louisiana. forests are cleared to provide space for cattle grazing. male children are encouraged to attend the university. the longest river on the continent is located here. birthdays are celebrated on january 1st. per capita income of northern buckland is more than $100,000.