What is the highest and the lowest total resistance that can be secured by the combination of four coils of resistance?
(a) Highest: Sum of all resistances; Lowest: 0
(b) Highest: Twice the resistance of the highest coil; Lowest: Half the resistance of the lowest coil
(c) Highest: Resistance of the highest coil; Lowest: Resistance of the lowest coil
(d) Highest: Resistance of the lowest coil; Lowest: Resistance of the highest coil
