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Behaviorists are interested in understanding the concepts or mechanisms that explain the process of classical conditioning.

Explanation
The concept of the unconditioned stimulus, unconditioned response, conditioned stimulus, and conditioned response can be understood with the help of the given examples:

The smell of delicious food makes people drool naturally. It does not require any association to be formed for the occurrence of the response. Therefore, in this case, food is the unconditioned stimulus, and people's response towards it [drooling] is the unconditioned response.

An electric shock is naturally distressful for an organism. If it is paired with a neutral stimulus [say a food item], an organism is prone to become aversive to that particular food item as well. Since in this case, food is not naturally aversive, it became aversive when it was presented with an electric shock, it would be called the conditioned stimulus. The response of aversion towards the food would be called the conditioned response.

Verified Answer
The following terms can be defined as:

1. Unconditioned Stimulus: The unconditioned stimulus can produce the response naturally without being conditioned.

2. Unconditioned Response: The unconditioned response is the one that comes naturally in the response of a stimulus before conditioning.

3. Conditioned Stimulus: The conditioned stimulus [previously a neutral stimulus] is the one that acts as an alarm for the occurrence of the unconditioned stimulus. Unless it is not associated with the unconditioned stimulus, it cannot produce a response.

4. Conditioned Response: The conditioned response is the one that gets evoked by the conditioned stimulus after the conditioning takes place.