The correct answer is A) using higher voltage and lower current. The reason this is the correct answer is that line losses in a distribution circuit are directly proportional to the square of the current and inversely proportional to the voltage. By using a higher voltage and lower current, the line losses can be minimized, as the current is reduced, thereby reducing the associated power losses. The other options are incorrect because: B) Using higher current and lower voltage would increase the line losses. C) Increasing the number of thermal relays does not affect the line losses. D) Adding rubber insulation conductors does not directly reduce the line losses.