Answer:
C. When the oceanic lithosphere, which is more dense, sinks and pulls the plate with it
Step-by-step explanation:
Slab pull and other mechanisms are responsible for the motion of plates. Every tectonic plate is driven by mantle convection. 
- Convection is a form of heat transfer in fluids. 
- It is as a result of differences in density and temperature values. 
- The oceanic crust is denser and colder. 
- As hot magma from deep within the subsurface rises and move through cracks, the oceanic lithosphere is drawn down and deeper. 
- This cycling between the cold lithosphere and hot rising plumes provides the mechanism that drives plate motion.