Final answer:
Heat transfer by conduction requires physical contact between the objects, as their atoms and molecules transfer energy through vibrations. Option A. touch is correct.
Step-by-step explanation:
For heat to transfer using conduction, things must touch. Conduction is the type of transfer where heat transfer occurs through stationary matter by physical contact. The atoms and molecules in the touching materials vibrate faster as they gain energy from the heat source, and this vibration and interaction between adjacent atoms transfer the heat. In contrast, processes like convection involve the macroscopic movement of a fluid, and radiation involves the transfer of energy through electromagnetic waves, both of which can occur without direct contact.