Final answer:
Heat cannot spread through a solid by convection because solids do not have the ability to flow like fluids. Heat in solids can only transfer through conduction.
Step-by-step explanation:
Heat cannot spread through a solid by convection because convection is the heat transfer by the macroscopic movement of a fluid, and solids do not have the ability to flow like fluids.
Conduction, on the other hand, is the heat transfer through physical contact between particles. In solids, the particles are closely packed and can transfer heat energy from one particle to another through collisions.
Therefore, heat can only spread through a solid by conduction, not by convection.