Due to a traffic jam, you have to considerably reduce the speed of your vehicle. Must you warn, whenever possible, the vehicles driving behind?
A)Yes, by using the emergency light.
B)No, warnings are prohibited, as they can create confusion.
C)Yes, by repeated use of the brake lights or by moving the arm alternately up and down.Correct
# Explanation
When you must considerably reduce speed due to a traffic jam, you must warn the vehicles driving behind by using the **brake lights** (which activate automatically) or by manual signals such as **moving the arm alternately up and down**. These actions are mandatory to avoid collisions. The emergency light is not the correct way to make this warning in this specific case.