Which term describes the boundary where one plate sinks below another?

• A. Subduction
• B. Seafloor Spreading
• C. Continental Drift
• D. Pangaea

Answer: (A)

Subduction describes the boundary where one tectonic plate sinks beneath another into the mantle. This happens at convergent boundaries and explains features like deep ocean trenches and volcanic arcs where the sinking plate melts and feeds volcanic activity. The other terms point to different processes: seafloor spreading forms new crust as plates move apart at mid-ocean ridges; continental drift is the overall movement of continents within the plate system; Pangaea is the ancient supercontinent that once combined many landmasses. Because the boundary in question specifically involves a plate sinking below another, subduction is the exact concept at work.