Aluminium is used in overhead transmission lines because it has:
Good electrical conductivity and low weight
Overhead transmission lines hang between towers over long spans, so the conductor must carry current efficiently and also be as light as possible to limit sag and tower loading.
Aluminium meets both needs: its electrical conductivity is high, only a little below copper, so it carries the line current with acceptable loss.
At the same time aluminium is roughly one-third the density of copper and cheaper, which reduces the weight the towers must support and the overall cost of the line.
An option claiming zero conductivity is wrong because such a material would not conduct at all and could carry no current.
High resistance with high weight, or infinite resistivity, would give large power losses and heavy unmanageable lines, the opposite of what is wanted.
So aluminium is chosen for the combination of good conductivity together with low weight.
Hence, the answer is Good electrical conductivity and low weight.
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