(A) Convection: In convection heat is transferred from one point to another by the actual motion of matter from a region of high temperature to a region of lower temperature. (B) The hot bar placed under running tap water loses heat within water. The warmer water rises up, this leads to circulation of heat from bar to water by the process of convection. Furthermore, heat will be transferred inside the molecules of the bar by conduction. Thus, the heat transfer when hot bar is placed under running tap water is due to both conduction and convection. (C) Heat can only be transferred between two systems due to their temperature difference in the form of radiations, molecular vibrations, molecular displacement etc.