When driving through heavy fog, you should:

Answer: B — Slow down

When driving through heavy fog, slowing down is the most critical step for maintaining safety. Reduced visibility in foggy conditions can significantly impair your ability to see other vehicles, road signs, and obstacles. By decreasing your speed, you allow yourself more time to react to any sudden changes or dangers in the environment. In addition, slower speeds make it easier to control your vehicle and maintain a safe distance from other cars. This is particularly important in fog, where depth perception can be distorted, making it difficult to judge how far away other vehicles are. Other options, like following closely behind another vehicle, could lead to dangerous situations if that vehicle suddenly stops or makes a sudden maneuver. Using bright lights increases visibility but can scatter light back into your eyes, further reducing your ability to see clearly. Turning on parking lights doesn't provide adequate visibility in fog—headlights are far more effective for seeing and being seen. Thus, slowing down is crucial for safety when navigating through thick fog.