The use of a choke coil fitted to fluorescent tubes is to control the current and prevent it from continuing to rise.

Option 1, "It steps down the line voltage," is incorrect as the primary purpose of a choke coil is to regulate current, not voltage.

Option 2, "It controls the current to prevent it from continuing to fall," is also incorrect because the choke coil does not prevent current from falling; its role is to stabilize and control the current.

Option 3, "It steps up line voltage," is not applicable to the use of a choke coil in fluorescent tubes.

The correct answer, option 4, states that the choke coil controls the current to prevent it from continuing to rise. This is accurate because the choke coil acts as an inductor to regulate the current passing through the fluorescent tube, ensuring a steady flow and preventing any fluctuations or surges in current.