The correct answer is letter D
Overt behavior is important, but also covert behaviors. The difference between open and covert behavior lies in the issue of accessibility. While open behaviors are subject to direct observation by two or more people, covert behaviors are subject to direct observation only by the person who lives the contingency.
The covert behaviors may have parts of the antecedent stimulus - response - reinforcing stimulus relationship as covert, in most cases only the responses are considered covert. These responses can be emotions, feelings, thoughts, dreams, fantasy.
