Final answer:
A fox that pants with its tongue out is likely regulating its body temperature and may be tired, not necessarily hungry, happy, or sad.
Step-by-step explanation:
When a fox pants with its tongue hanging out of its open mouth, it is typically a sign that the fox is regulating its body temperature. Unlike humans, many animals pant to cool themselves down because they do not have as many sweat glands to help with temperature regulation. Panting allows them to evaporate moisture from the lungs and tongue which cools them down effectively. In the context of the options provided, the most accurate answer is that the fox is likely tired due to exertion or heat, which could also be associated with being hot or overheated, rather than being hungry, happy, or sad. The other information about a frog's tongue or the emotional states of birds does not relate directly to a fox's behavior when panting.