The correct answer is A. 150 to 220 kV.
The higher the transmission voltage, the lower the current for the same amount of power. This means that the losses due to resistance in the transmission lines are lower. For a transmission distance of 500 km, a transmission voltage of 150 to 220 kV is typically used.
Option B is incorrect because it is too low. A transmission voltage of 100 to 120 kV would result in too much current and too much loss.
Option C is incorrect because it is too high. A transmission voltage of 60 to 100 kV would not be efficient for a transmission distance of 500 km.
Option D is incorrect because it is too low. A transmission voltage of 20 to 50 kV would result in too much current and too much loss.