Answer:
A. a place where one plate is pushed down under another such that is melts down into the mantle.
Step-by-step explanation:
Subduction is a type of convergent boundary that occurs when one plate is denser than another and therefore sinks below it. This occurs when an oceanic plate converges with a continental plate. The oceanic plate is denser than the continental plate above it, and it sinks, forming a trench. As the plate sinks, the rock is melted and is often forced back up through volcanoes that appear along the shoreline. The Mariana's Trench is a famous example of a geological feature formed at a subduction zone.