Which of the following can cause radio frequency interference?

Radio frequency interference (RFI) can be caused by several different mechanisms. Fundamental overload occurs when a strong, legitimate signal overwhelms a nearby receiver's front end, even if that receiver is tuned to a completely different frequency. This is primarily a deficiency in the receiving equipment's filtering. Harmonics and spurious emissions are unintended signals generated by the transmitter itself. Harmonics are multiples of the operating frequency, while spurious emissions include other unwanted signals transmitted outside the intended channel. Since all three of these phenomena are well-known causes of RFI, the correct choice includes all of them.