Which of the following would reduce RF interference caused by common-mode current on an audio cable?

Common-mode current happens when unwanted RF travels along the outside shield of a cable, effectively turning it into an unintended antenna. This is a frequent cause of RF interference (RFI) in audio cables and station wiring. Placing a snap-on or toroid ferrite choke around the cable adds inductive reactance to the exterior of the line. This acts like a resistor to the unwanted RF, choking off the common-mode current without disrupting the differential audio signal flowing inside. Shorting the center conductor to the shield would completely destroy the audio signal, and adding plastic insulation does nothing to stop RF energy.