Answer: A. After he won the Nobel Prize for this discovery
Explanation: Ivan Pavlov was a Russian scholar who was to devote himself to religion because his father was a priest. However, he decided to abandon it and devote himself to the science, specifically, the study of the digestive system in mammals. In 1904, he was awarded the Nobel Prize in this field, and then devoted himself to conditioned behaviour in animals, more specifically in dogs. He practised conditioned dog behaviour for the rest of his life in 1936. His experiments with dogs made a significant contribution to this area and paved the way for further later research on the subject.