Final answer:
The BT used a gestural prompt by pointing to the blue block to indicate the correct response to the client in the Discrete Trial Teaching session.
Step-by-step explanation:
The behavior technician used a gestural prompt to teach the client to identify the color blue by instructing the client to hand her the "blue block" and then pointing to it. A gestural prompt involves using physical movements or gestures to indicate the desired response without physically guiding the person. This form of prompting is often used in Discrete Trial Teaching (DTT), which is a structured ABA (Applied Behavior Analysis) technique used to teach a skill in a step-by-step, simplified and reinforced manner.