Power is transmitted over transmission lines on high voltage, because-

Correct option is D

Explanation:
1. Current is reduced: When power is transmitted at high voltage, the current in the transmission lines is reduced for the same power level. This is because power P=VI, where V is voltage and I is current. If V is increased, I can be reduced for the same P.
​Efficiency is increased: Lower current results in lower power losses due to resistance in the conductors, as power loss is given by $$P_{Loss}= I^2 R$$ Reducing the current reduces the $$I^2 R$$. losses, thereby increasing the efficiency of power transmission.

Conductor cost is reduced: With lower current, the cross-sectional area of the conductors can be smaller, which reduces the amount of material needed and hence the cost of the conductors.​

Transmitting power at high voltage addresses both efficiency and cost concerns, making option (d) the correct answer.