which statement describes one event that happens at deep - ocean trenches?\ncrust is formed.\nmountains are…

Brief Explanations:

Deep - ocean trenches are formed at convergent plate boundaries where the denser oceanic plate subducts (slides under) the lighter continental plate or another less - dense oceanic plate. Crust is formed at mid - ocean ridges, mountains can be formed in various ways like at convergent boundaries but not specifically the main event at trenches, and seafloor spreading occurs at mid - ocean ridges.

Answer:

D. Denser plates slide under lighter plates.