Answer:
neutral stimulus; unconditioned stimulus
Step-by-step explanation:
Neutral stimulus and unconditioned stimulus are two different parts involved in the classical conditioning theory that was developed by Ivan Pavlov who was considered as one of the greatest psychologists and behaviorists of his times while conducting his experiment on dogs.
A neutral stimulus is described as a stimulus that doesn't produce any particular response except focusing on attention. Once the neutral stimulus gets connected with an unconditioned stimulus gives rise to a conditioned stimulus.
An unconditioned stimulus is described as a stimulus that is responsible for triggering a particular response automatically, unconditionally, and naturally.