The correct answer is A: Each transmitter that produces 20 percent or more of its MPE limit in areas where the total MPE limit is exceeded. When evaluating a site with multiple transmitters operating at the same time, the operators and licensees of each transmitter that produces 20 percent or more of its MPE limit in areas where the total MPE limit is exceeded are responsible for mitigating over-exposure situations. When multiple transmitters contribute to RF exposure, you must evaluate the total exposure. If the total exceeds MPE limits, then each transmitter contributing 20% or more of its own MPE limit is responsible for helping to reduce the exposure. This ensures that significant contributors share responsibility for compliance. Transmitters contributing less than 20% are considered minor contributors and aren't required to take action. This rule prevents any single operator from being solely responsible when multiple stations contribute to over-exposure.