Fluorescent tubes are fitted with a choke. The choke coil:

The correct answer is (D) Reduces current in the circuit. The choke coil acts as a ballast in a fluorescent tube—it limits and controls the current, preventing damage to the tube once it starts glowing.

In a fluorescent tube, once the gas inside is ionized, the resistance of the tube goes down drastically. If the current is not regulated, it would rise dangerously and harm the tube. This is where the choke coil (ballast) enters the picture:A choke is an inductor in series with the tube. An inductor resists changes in current (because of self-induction). Therefore, when the current tries to increase, the choke resists and reduces the current flowing in the circuit.