An inductor blocks AC but allows DC to pass.
An inductor resists a change in current that is why it blocks AC. The equation of an inductor is $2058_w58_h38.png$ . If you apply DC across an inductor, it will stabilize to some current flow based on the maximum current available from the current/voltage source. In this mode, the inductor presents very low resistance, so it can be said that it allows DC to pass.
B An inductor blocks DC but allows AC to pass.
C An inductors blocks both AC and DC.
D An inductor allows both AC and DC to pass.