The correct answer is: D. No insulation is required
AC.S.R. Conductors are made up of an aluminium core surrounded by a steel tape. The steel tape provides strength and corrosion resistance, while the aluminium core provides conductivity. The two materials are bonded together without the need for insulation.
Insulating the aluminium core from the steel tape would not provide any benefit, as the two materials are not in contact with each other. In fact, insulation would actually make the conductor more difficult to manufacture and would increase its cost.
Therefore, the correct answer is: D. No insulation is required.