Which of the following actions must be completed before changing lanes?

Answer: B — Checking blind spots

Before changing lanes, checking blind spots is a critical action that must be completed to ensure safety on the road. Blind spots are the areas around your vehicle that are not visible through your mirrors. By turning your head and checking these areas, you can confirm whether another vehicle is present and avoid a potential collision. This step is essential because relying solely on mirrors may not provide a complete view of the road conditions, especially if a vehicle is positioned closely behind or alongside you. While other options, such as looking at speed limit signs, turning on your headlights, and adjusting your rearview mirror, may contribute to safe driving practices, they do not directly address the immediate risk of changing lanes. It's the check for vehicles in your blind spot that actively helps to prevent accidents during this maneuver.