The correct answer is: A. nuclear power plants
Nuclear power plants have the lowest fuel transportation cost because they do not require fuel to be transported to the plant. Nuclear power plants use uranium as their fuel, which is a naturally occurring element that is mined. Once uranium is mined, it is transported to a processing facility where it is converted into uranium oxide. The uranium oxide is then transported to the nuclear power plant, where it is used to generate electricity.
Diesel generating plants and steam power stations require fuel to be transported to the plant. Diesel generating plants use diesel fuel, which is a petroleum product that is transported by truck or rail. Steam power stations use coal, which is a fossil fuel that is transported by truck or rail.
Therefore, nuclear power plants have the lowest fuel transportation cost because they do not require fuel to be transported to the plant.