During the process of mountain building a. material from the earth's interior is often returned to the surface. b. the earth's interior often gains material from the atmosphere. c. weathering and erosion to generate igneous rock formations. d. material from the earth's surface is often broken down by crystalization.

A. material from the Earth's interior is often returned to the surface

Explanation:

The mountains are formed when there is two plates colliding, especially when it comes to two continental plates. Because none of the plates has the tendency to sink below the other plate, their collision creates enormous amount of pressure on the crust around the boundary.

That enormous pressure manages to push the crust upward, and slowly mountain ranges start to form as the crust gains on elevation. While this process goes on, lot of material that has been buried deep into the interior of the Earth for millions of years, starts to come out on the surface.

That makes up for lot of disturbance in the rock strata, and makes up fro interesting and unexpected things. A good example of this are the Himalayas, as there are oceanic sediments at the top parts of them, despite the mountains being more than 8,800 meters high.