Which of the following could be a cause of interference covering a wide range of frequencies?

Arcing at a poor electrical connection acts exactly like a primitive spark-gap transmitter. As the electrical current jumps the gap, it creates a sudden, sharp impulse of energy that splatters across a massive portion of the radio spectrum, resulting in severe broadband interference. Other options, such as failing to use a balun on a balanced antenna, can cause RF to travel down the outside of a feedline (common-mode current) and radiate into the local shack. However, this type of interference will be limited to the specific frequency being transmitted, rather than spanning a wide range of frequencies.