Millie Feels Sick Every Time She Travels by Air

Millie feels sick every time she travels by air.She associates flying with physical illness and,as a result,hates air travel.She also finds it difficult to watch movies with airplanes or read books about airplanes because they make her feel unwell.In this scenario,Millie is demonstrating learning through:

A) positive reinforcement.
B) classical conditioning.
C) observational learning.
D) implicit learning.