Explanation: When evaluating RF exposure at sites with multiple transmitting antennas, the FCC requires that all antennas contributing more than **5%** of the maximum permissible power density exposure (MPE) limit at a specific location must be included in the cumulative RF exposure calculations. This **5%** threshold (Answer B) is a practical rule set by the FCC to ensure that significant contributors to the overall RF field are accounted for, while avoiding the overly complex and often negligible contributions of very low-power or distant sources. It balances safety by requiring analysis of all relevant emitters with the practicality of site evaluation. * **A) Any:** Requiring "any" contribution would be impractical and overly burdensome, as even extremely distant or low-power sources would need analysis. * **C) 1%:** While more conservative, the FCC has determined that 5% is a sufficient threshold for safety without undue complexity. * **D) 12.5%:** This threshold would be too high, potentially omitting sources that could contribute meaningfully to the total cumulative exposure, thus potentially underestimating the overall RF field and compromising safety.