The correct answer is D: Points with constant reactance. The arcs on a Smith chart represent points with constant reactance. Each arc shows all impedances that have the same reactance value (but different resistance values). The Smith chart has two families of curves: resistance circles and reactance arcs. The arcs are curved lines representing constant reactance. Inductive reactance arcs are in the upper half of the chart (+j values), and capacitive reactance arcs are in the lower half (-j values). All points on a given reactance arc have the same reactance but different resistance values. For example, the +j50-ohm reactance arc contains all impedances with +j50 ohms reactance (like 25+j50, 50+j50, 100+j50, etc.).