The correct answer is A. Radial system.
A radial system is the simplest and lowest in first cost because it has the fewest components. It consists of a single source of power, such as a generator, and a number of loads connected to it by branches. The power flows from the source to the loads in a single direction.
A ring system is more complex than a radial system because it has two or more sources of power and the loads are connected in a loop. This allows for redundancy in the system, so that if one source of power fails, the other source can take over. However, it also makes the system more expensive to install and maintain.
An interconnected system is the most complex type of DC distribution system. It consists of a number of radial systems that are connected together. This allows for the sharing of power between the systems, which can improve reliability. However, it also makes the system more expensive to install and maintain.
In conclusion, the radial system is the simplest and lowest in first cost because it has the fewest components. It consists of a single source of power, such as a generator, and a number of loads connected to it by branches. The power flows from the source to the loads in a single direction.