The correct answer is B) using higher voltage and lower current. The reasoning behind this is that in a distribution circuit, the line losses are proportional to the square of the current flowing through the conductors. By using a higher voltage and lower current, the amount of current flowing through the conductors is reduced, which in turn reduces the line losses. This is in accordance with the principles of electrical power transmission, where higher voltages are preferred to minimize losses in the distribution system. The other options are incorrect because A) using higher current and lower voltage would increase the line losses, C) adding rubber insulation conductors would not directly reduce the line losses, and D) increasing the number of thermal relays would not affect the line losses in the circuit.