Answer: A. the transfer of heat by currents
Explanation: There are three modes of heat transfer:
1) Conduction: This type of heat transfer happens when there is direct contact between the two object. Example: heating a pan on stove.
2) Convection: This type of heat transfer happens when there is a movement of fluid (liquid or gas) due to the movement of hot layers to the top and cold layers to the bottom which leads to convection currents. Example: Heating of swimming pool.
3) Radiation: This type of heat transfer happens when there is direct transfer of energy through space. Example: Heating of earth's surface.
B. The transmission of heat across matter is conduction.
C. The electromagnetic radiation from the surface of an object which is due to the object's temperature is radiation.
D. The transmission of heat across empty space is radiation.
