Answer: Professor Rochelle's door being open was a (A.) discriminative stimulus for asking questions.
Explanation: A discriminative stimulus is a term used to refer to the act of inducing someone to do a particular thing. In that way, this type of stimulus has the power of influencing an individual's behaviour. Moreover, a discriminative stimulus increases the chances that this individual will act as expected. Therefore, by leaving her door open, Professor Rochelle is inducing her students to ask questions, that is to say that she leaves the door open in order to make her students behave in a particular way, which is to ask questions.