Letter A is the correct answer.
Even though John B. Watson is considered to be father of behaviorism, Burrhus Frederic Skinner was the one who proposed the most extreme form of behaviorism which later was known as "radical behaviorism". Skinner was a North-american psychologist, Harvard professor, author and social philosopher. He published over 20 books and 180 articles and is well-known as the most influential psychologist of the 20th century.
