The most influential early research on operant conditioning was conducted by who?

The correct answer is B. Skinner.

B.F. Skinner is widely recognized for his research on operant conditioning, a learning process through which the strength of a behavior is modified by reinforcement or punishment. His experiments with animals, particularly using a device known as the Skinner box, laid the foundation for our understanding of behavior modification and learning principles in psychology. If you have more questions or need further clarification, feel free to ask!