The area of land where water is drained downhill into a body of water is known as a drainage basin, or

Watershed

A watershed or drainage basin is a down the slope land where the water is drained off from sources of water flowing comparatively at some elevation. It includes water from rivers, river streams that progressively drain into larger areas. The initial source of watershed is called as headwater. The endpoint of watershed is open up into another water body is called as mouth.

layer a is the exosphere and layer b is the thermosphere.   is the answer i think but i hope this .

it breaks and dirupture other materials and other sencews from the bottom