After making a coupling, what is the immediate action required?

Answer: B — Stretch slack

After making a coupling, the immediate action required is to stretch slack. This process involves ensuring that any slack in the train's couplers is taken up, which helps achieve a firm connection between the cars. Stretching the slack is critical because it aligns the cars properly and sets them in motion safely. This step is fundamental to maintaining a secure and effective coupling before additional actions, such as inspecting other elements or checking brake systems, can be performed reliably. By stretching the slack, the cars engage fully, allowing for the proper operation of the air brake system and ensuring that all components function seamlessly together. This initial step contributes to the overall safety and efficiency of train operations, setting a solid foundation for subsequent checks and adjustments.