To ensure that vehicles following us can see us in case of **fog**, it is essential to use the **rear fog light**. This light is **red** and is specifically designed to improve the visibility of our vehicle from behind in low visibility conditions, such as fog, snow, heavy rain, or smoke.

- The **rear fog lights** are crucial in situations where visibility is very reduced. They should only be used when weather conditions require it, as their intensity can dazzle other drivers if used incorrectly.

- Unlike the front fog lights, which are white or yellow and help us see the road ahead better, the rear lights are intended for other drivers to see us.

Therefore, in foggy situations, the **rear fog light** is the appropriate option to ensure that vehicles coming from behind can see us clearly.