The answer is conduction. Conduction is the process that requires 2 object in contact with each other.
The three main types of heat transfer are convection, conduction, and radiation.
Convection only happens in fluid states, which means gas or liquids. In convection, the fluid goes in circular motion so that all the areas can be heated up. As they work in fluid only, so it does not match with the question.
Radiation happens everywhere, even in vacuum state. The sun heats the earth by radiation too as there’s no air for convection and no objects in contact. So, radiation is not correct too.
Conduction is correct because when two objects are in contact, the atoms moves and collide with each other to pass on the energy, heat always transfer from the hotter object to the colder object.
