Explain, incorporating the process of fermentation, why he/she is experiencing the burning sensation

Because of anaerobic energy production lactate accumulates in muscles, increases acidity  and cause burning sensation.

Explanation:

If someone performs excessive exercise, needs more oxygen for muscles to work. In scarcity of oxygen muscles generates energy anaerobically from glucose.

In plenty of oxygen cells undergo aerobic pathway and produce much energy comparison to anaerobic pathway. When oxygen is not present or limited then pyruvate converts into lactate and accumulate in the muscle . Production of lactic acid in anaerobic condition; LACTIC ACID FERMENTATION cause   burning sensation.

you didn't give any options but heres what i can tell you: an inference is likely to change based on additional observations. the latter is something that you have seen or sensed using your sensory organs while the former is like a conclusion out from what you have observed.