Answer:
Classical conditioning
Explanation:
Classical conditioning refers to an automatic reaction known as classical response or behaviour learnt over a period of time that arises from the input of a conditioned stimuli and a neutral stimulus.
Sarah feeling sick every time she travels by air is a conditioned response that was as a result of air travel. She also feels uncomfortable around things to do with airplanes. The feelings here is a conditioned response from a conditioned stimuli (the airplanes)