According to the Definition of Learning, How Could a Researcher

According to the definition of learning, how could a researcher ever show that cognitive learning had taken place in a subject?

A) By measuring a behavioural change that could directly be tied to a previous experience
B) The researcher would have an intuitive feel for the amount of learning the subject had experienced.
C) Through the process of elimination - by showing that the person had not learned through classical or instrumental conditioning.
D) Only by asking the subject if he or she had learned something
E) By measuring the brainwave pattern of the subject