Watson Found Pavlov's Conditioned Reflex Concept Useful in His Own

Watson found Pavlov's conditioned reflex concept useful in his own work because:

A) it was a properly objective technique that he could apply to many other learning situations besides the salivary reflex.
B) it explained a great deal about the nature of the brain.
C) it showed the value of precise measurements in psychological experiments.
D) both a and b above