The correct answer is A) discriminative stimulus; asking questions.
Professor Rochelle told her students that if her door was closed it meant that she was unavailable to them and would be angry if they knocked on her door. But if her door was open, it meant that she was in a rare good mood and would answer questions at that time. Professor Rochelle's door being open was a discriminative stimulus for asking questions.
A discriminative stimulus, according to Malott, "is the type of stimulus in the presence of which a particular response will be enforced." Discriminative stimulus establishes the atmosphere for behaviors that have been reinforced in past times. In this case, the teacher has had episodes of anger when students interrupt her while her door's office was closed, so students know that when that door is closed, they are not allowed to interrupt.
