The correct answer is: A. 20 – 25 km.
Transmission voltage of 11 kV is normally used for distances up to 20-25 km. This is because the higher the voltage, the lower the current required to transmit the same amount of power. This means that there is less loss of power due to resistance in the transmission lines. However, higher voltages also require thicker and more expensive transmission lines. Therefore, 11 kV is a good compromise between power loss and cost for distances up to 20-25 km.
Option B, 40-50 km, is incorrect because the loss of power due to resistance in the transmission lines would be too high. Option C, 60-70 km, is incorrect because the transmission lines would be too expensive. Option D, 80-100 km, is incorrect because the loss of power due to resistance in the transmission lines would be too high and the transmission lines would be too expensive.