Which of the following components should be added to an inductor to increase the inductance?

Inductors in series add their inductance values together, acting exactly the same way resistors do. The formula for total series inductance is simply L_total = L1 + L2 + L3... Therefore, adding an inductor in series is the correct way to increase the overall inductance of a circuit. Conversely, adding an inductor in parallel decreases the total effective inductance. Adding a capacitor, whether in series or parallel, changes the circuit into an LC resonant circuit rather than purely increasing the inductance, making those options incorrect.