Answer:
A). External noise.
Step-by-step explanation:
'External noise' is demonstrated as the noise which ensues in the surroundings instead of the individual(speaker) himself/herself. Such noise could be very distracting as well as disturbing at the same time that may prevent a person from concentrating on a specific goal or objective.
In the given situation, Jason similarly experiences the 'external noise'(environmental factors) that averts him from paying attention to the lecture delivered by the Professor in the class. The environmental factor('uncomfortably warm') interferes/distracts him and hampers his concentration. Therefore, option A is the correct answer.