When one continental plate slides beneath another a. weathering and erosion work to build high plateaus and mountain ranges. b. the process of melting returns material to the earth's surface. c. material from the earth's interior is always returned to the surface. d. material from the earth's surface is returned to the interior.

The answer is D. The submerged tectonic plate (usually the ocean plate since it is denser) is subjected to high pressure and temperatures and begins to melt as a result of the compression. It is also melted by the heat of the mantle. The melted plate then falls into the mantle where it melts and becomes part of the liquid mantle. The magma, over years, may  reach the earth’s surace either through a volcanic activity or in areas of sea-floorspreading.

it has to be b, about 97 percent.