Which of the following is a discriminative stimulus (SD) ?

Receiving a sticker for completing a task

Receiving something to eat after saying "I'm hungry"

Saying "Match blue" and receiving a blue card

Not following a direction given by an adult

Saying "Match blue" and receiving a blue card

Explanation:

A discriminative stimulus is a stimulus like a place, people or thing which causes a forced behavior of reinforced behavior. This reinforced behavior is not necessarily observed in stimulus behavior.

In the given question, the person wanted the match for blue color (stimulus) and received a blue card (reinforcer). In this situation since the person wanted the match for the blue color and received it as well, therefore, a reinforced behavior is expected in the case as the person got what he wanted.

Thus, Saying "Match blue" and receiving a blue card is correct.