c is one reason. But actually aluminum is a better conductor than copper when you measure conductivity per unit weight. And per unit weight is the true measurement when running heavy wires above ground, you want the the wire to be a light weight as possible.
The real answer is: none of the above.
The truth is more complicated. Conductivity is not the deciding factor. The deciding factor is total cost of electricity transmitted over time. There would be less electricity lost with copper but the cost of buying the copper and putting up the transmission lines would be much higher. The Al conductors have more electricity loss but they are not very strong so they require additional steel cable for strength. So... the calculation of the total costs to deliver electricity to customers over the expected life of the transmission lines is lowest with the Al-steel combination.
Aluminum is cheaper for the conductor. Transmission lines normally have a steel core for the load carrying or strength capability. Copper has become a popular target for thieves.
c).AL [sic: Al] is light in weight
If copper were used, more towers would be needed because they would have to be spaced a shorter distance apart in order to be able to support the extra weight from the copper wire. More towers = more money, so it's more economical to use aluminum..
a) Al is cheaper than Cu
C lighter.
a).AL is cheaper than CU b).CU is not available c).AL is light in weight d).AL is easily available
