The right answer is Conduction.
Thermal conduction (or thermal diffusion) is a mode of thermal transfer caused by a temperature difference between two regions of the same medium, or between two media in contact, and being realized without global displacement of material (on a macroscopic scale ) as opposed to convection which is another heat transfer. It can be interpreted as the transmission from near to thermal agitation: an atom (or a molecule) gives up some of its kinetic energy to the neighboring atom.
Thermal conduction is a process of internal energy transport linked to molecular agitation and due to heterogeneity of the medium on a macroscopic scale.
