Some transport vehicles have additional yellow lights. This is done because

The additional yellow lights on some transport vehicles serve a specific purpose:

Visibility in Fog:
Yellow lights are used on transport vehicles because they are more effective at piercing through fog and haze compared to white or other colored lights. This is due to the wavelength of yellow light, which is longer than that of white light.
Longer wavelength light, such as yellow, is less scattered by water droplets in the air, allowing it to penetrate the fog more effectively. This increased visibility helps the driver and other road users to see the vehicle more clearly, improving safety on the road.

Not for Aesthetics or Energy Efficiency:
The use of yellow lights is not primarily for aesthetic reasons or to save electrical energy. While yellow lights may have a distinct appearance, the main purpose is to enhance visibility and safety, especially in poor weather conditions like fog.
Therefore, the correct answer is [C] Yellow light pierces the fog making the road clearly visible.