Answer:
The association that Nasim made between eating the burger and feeling sick required only a single US-CS pairing.
Explanation:
The theory of classical conditioning was produced by Russian psychologist Ivan Pavlov to explain different aspects of human psychology. He explained how an unconditioned stimulus when paired with conditioned stimulus produce conditioned response. According to the question, question sickness due to burger was an unconditioned stimulus which is paired by Nasim to the burger (conditioned stimulus) and his feeling of sickness every time he saw a burger is conditioned response.