Final answer:
The subject of the question is Physics. The experiment described in the question is about determining whether the outside temperature is higher or lower than 0 °C (32°F) without using a thermometer. Therefore, the correct answer is A. Physics experiment.
Step-by-step explanation:
The subject of the question is Physics.
The experiment described in the question is about determining whether the outside temperature is higher or lower than 0 °C (32°F) without using a thermometer. This falls under the field of Physics because temperature measurement and understanding heat transfer are concepts in Physics.
Therefore, the correct answer is A. Physics experiment.