Question

which statement describes one event that happens at deep-ocean trenches?
○ crust is formed.
○ mountains are formed.
○ seafloor spreading occurs.
○ denser plates slide under lighter plates.

Explanation:

To solve this, we analyze each option:

• "Crust is formed" occurs at mid - ocean ridges (seafloor spreading creates new crust), not deep - ocean trenches.
• "Mountains are formed" at convergent boundaries can form mountains on land (like the Himalayas) or island arcs, but the main event at deep - ocean trenches is subduction, not mountain formation as the primary event.
• "Seafloor spreading occurs" at mid - ocean ridges, where new oceanic crust is created.
• "Denser plates slide under lighter plates" (subduction) happens at deep - ocean trenches. Oceanic plates (denser) subduct under continental or other oceanic plates (lighter in relative density in the case of oceanic - continental convergence) at deep - ocean trenches.

Answer:

Denser plates slide under lighter plates.