Where does sea-floor spreading take place? a. convergent boundaries c. oceanic volcanoes b. transform boundaries d. mid-ocean ridges

The right option is; d. mid-ocean ridges

Seafloor spreading is a geologic process that occurs at mid-ocean ridges, in which there is separation of tectonic plates (large slabs of earth's lithosphere) from each other. Seafloor spreading occurs due to mantle convection (circulation of heat by movement of materials in the earth’s mantle). A mid-ocean ridge is an underwater mountain range that is created due to volcanic eruptions. A mid-ocean ridge usually occurs where tectonic plates split apart.  

d.) greenhouse gases