Here is your answer:
Your answer is A conduction.
Reason: Conductions is when for example boiling water you put a metal spoon in the boiling water within seconds the spoon is hot that's because the heat from the boiling water transfered into the spoon making it hot! Also its not convection because it can't no be transfered between a solid an in the questions it has the word "solid" its also not D because that's when something or someone is under a lot of heat making them hot within minutes and when it came down to rather conduction and insulation I choose conduction because insulation is used for medicines!
Your answer is A.