If a thermal conductor is exposed to a source of heat then that conductor may become hot.
Copper is a great thermal conductor.
If copper is exposed to a source of heat then that conductor may become hot.
If what is exposed to a source of heat then that conductor may become hot?

[1] Energy.
[2] heat sources
[3] energy
[4] coal
[5] an object
[6] copper
[7] plastic
[8] thermometers