The correct answer is A) no ground-faults exist. If all the ground detection lamps burn with equal brilliance regardless of whether the test button is depressed or released, this indicates that there are no ground-faults present in the system. The equal brightness of the lamps signifies that the ground detection circuit is functioning properly and there is no abnormal grounding condition. The other options are incorrect because: B) a ground-fault in all phases would cause unequal brightness of the lamps, C) a high impedance ground-fault would also result in unequal lamp brightness, and D) a "dead" ground-fault, meaning no ground-fault at all, would not cause the lamps to burn equally.