The correct answer is A) open the circuit breakers on the distribution panel, one at a time, until the lights no longer indicate a ground. This is the correct procedure because it systematically isolates the grounded circuit by removing power from each circuit individually. By opening the circuit breakers one by one, you can identify which circuit is causing the ground indication on the main electrical switchboard. This is the quickest and most effective way to locate the grounded circuit. The other options are not as efficient. Option B, tracing the circuit paths, can be time-consuming and may not identify the exact location of the ground. Option C, checking circuit resistances, requires additional equipment and may not provide a clear indication of the grounded circuit. Option D, checking all circuits for continuity, is not specific enough to pinpoint the issue.