Final answer:
The cooling rate is directly proportional to the surface area.
Step-by-step explanation:
The cooling rate is directly proportional to the surface area.
This means that as the surface area increases, the cooling rate also increases.
For example, if you have two objects with the same temperature difference and thermal conductivity, but one has a larger surface area than the other, the object with the larger surface area will cool down faster.
Therefore, the answer to your question is: a) r