According to sea-floor spreading, where is old oceanic crust eventually destroyed?

Correct answer: In deep ocean trenches at convergent boundaries

The direct answer is B: in deep ocean trenches at convergent boundaries. Sea-floor spreading occurs when new oceanic crust forms at mid-ocean ridges as magma rises and cools. Step by step: a ridge creates new crust; plates move away from the ridge; with time, older oceanic crust becomes cooler and denser; when it meets another plate at a convergent boundary, the dense oceanic plate can sink beneath the other plate; this process is subduction and commonly occurs at deep-sea trenches, where the old crust is recycled into the mantle. Option B is correct. Option A is wrong because mid-ocean ridges are mainly places where new crust forms, not where old crust is destroyed. Option C is not a general destruction zone. Option D is wrong because continental plateaus are not the usual sites of oceanic-plate subduction. Memory cue: ridges make, trenches take.