While micro-analyzing the theoretical, experimental, and functional nature of the 'Classical Conditioning Theory' propounded by Ivan Pavlov and the 'Operant Conditioning Theory' by B.F. Skinner, which of the following statements most accurately defines the most fundamental and scientific difference between these two theories?

Classical Conditioning and Operant Conditioning are two major behaviorist theories of learning. In Pavlov's classical conditioning, the stimulus (such as food or bell) comes first and the reaction (salivation) occurs as its effect, which is called S-R (Stimulus-Response) learning. In contrast, in Skinner's operant conditioning, the organism acts independently in its environment (Response) and based on the consequences (such as reinforcement in the form of receiving food), the frequency of that behavior is determined, which is called R-S (Response-Stimulus) learning.