D) convection! here is the reason why :the definition of convection is the concerted, collective movement of groups or aggregates of molecules within fluids (e.g., liquids, gases) and rheids, through advection or through diffusion or as a combination of both of them. So becuase the medal is more convective, this causes it to be heated faster!
Note; this is why we use glass heating plate, so they dont get hot and burn people