Answer:
Oceanic ridges and
Deep sea trenches.
Step-by-step explanation:
DEEP SEA TRENCHES are places where the speeding sea floor runs out of room and the ocean plates are subducted, form where crustal plates plunge back into the mantle.
OCEAN RIDGES are spreading centers; that is, they are divergent plate boundaries where magma wells up from below. Where new crust is being formed.