The correct answer is A. Single side lighting.
Single side lighting is the most economical lighting layout which is suitable for narrow roads. It is a simple and effective way to light a road, and it can be installed quickly and easily. Single side lighting is also relatively inexpensive, making it a good option for budget-minded projects.
Staggered system and central lighting system are more complex and expensive than single side lighting. They are also less effective in lighting narrow roads. Staggered system is a type of lighting system in which the lights are placed on opposite sides of the road. This type of system can be effective in lighting wide roads, but it is not as effective in lighting narrow roads. Central lighting system is a type of lighting system in which the lights are placed in the center of the road. This type of system is also not as effective in lighting narrow roads as single side lighting.
In conclusion, single side lighting is the most economical lighting layout which is suitable for narrow roads. It is a simple, effective, and inexpensive way to light a road.