Answer:
Pavlov was studying salivation in dogs as part of a research program on digestion.
Explanation:
Ivan Pavlov discovered the concept of conditioning of reflex actions in dog when he was conducting a study on salvation in dogs.
He noticed that the dog (he was experimenting) start salivating as it hears the footstep of assistant that brings food. This made Pavlov to discover conditional stimulus.
Here the conditional stimulus was the sound of foot steps of assistant (as this was associated with the food) and the conditional response was salvation.
In normal cases, food is an unconditioned stimulus that produces unconditional response i.e salvation in dogs.
Hence, the correct statement is
"Pavlov was studying salivation in dogs as part of a research program on digestion."