Answer:
A. the international date line
The density of air in a limited amount of space.
Based of the map, you can infer that it's D because if you look the rivers are running through multiple countries and act as a border for the countries of Germany, Austria, Hungary, etc.
hopefully this helps
Answer:
I'm pretty sure it gets through these joint type things that connects the cave to the surface
Explanation:
Hope this helps:)....if not then sorry for wasting your time and may God bless you:)
The continental drift theory
