In sea-floor spreading, molten material rises from the mantle and erupts
a. along the edges of all the continents.
b. along mid-ocean ridges.
c. in deep-ocean trenches.
d. at the north and south poles.

A ridge forms along a crack in the oceanic crust. At a mid-ocean ridge, molten material rises from the mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge. ... This process, called sea-floor spreading, continually adds new material to the ocean floor.