I would say a because that is the only one that makes sense but I’m not 100% sure
<span>At mechanical waves need a medium to travel in order to transport their energy from one location to another.
</span><span>Mechanical waves require a medium to travel through so that they can transmit energy. Some examples of mechanical waves are water waves, sound waves and the waves of a slinky or jump rope. The medium through which a mechanical wave moves through can be a fluid, solid or gas.</span>
if it is heat flow through a metal, it would be necessary to have a conductor so that the electrons can flow through it (delocalised electrons).
In terms of radiation, it would require a good absorber of heat (e.g. a black surface) so that the thermal energy flows through on the surface area.
The answer for this question is: C
