Multi-core cables generally use

Square conductors
Circular conductors
Rectangular conductors
None of the above

The correct answer is: B. Circular conductors

Multi-core cables generally use circular conductors because they are more efficient in terms of space and weight. Circular conductors also have a lower resistance than other shapes, which means that they can carry more current without overheating.

Square conductors are less efficient in terms of space and weight, and they also have a higher resistance than circular conductors. Rectangular conductors are somewhere in between circular and square conductors in terms of efficiency and resistance.

None of the above is not a correct answer because it does not specify a particular shape of conductor.