Form at convergent boundaries, and form at divergent boundaries. a. cracks, volcanoes c. volcanoes, cracks b. volcanoes, mid-oceanic ridges d. mid-oceanic ridges, cracks select the best answer from the choices provided a b c d

b. volcanoes, mid-oceanic ridges

Explanation:

Convergent boundaries occur where lithospheric plates collide head-on, with consequences that depended on the differences in plate density. Generally the highest density plate plunges under the other, partially fuses in depth and generates large volumes of magma and lava, such as, for example, on the peaceful margin of South America, between the Nazca and South American plates.  It is from this kind of boundary that volcanoes arise.

At the divergent boundaries, two plates move away from each other and the space produced by this spacing is filled by a new magmatic crust material. Thus, the divergent boundary is constructive, since it allows the expansion of the ocean floor, originating meso-oceanic chains and consequent formation of a new lithosphere.