The correct answer is D) .016 of a second. In a 60 Hz AC system, the duration of one complete cycle is the reciprocal of the frequency, which is 1/60 seconds or 0.016667 seconds. This is because in a 60 Hz system, there are 60 complete cycles per second, so the duration of each cycle is 1/60 of a second, or approximately 0.016 seconds. The other answer choices are incorrect because: A) 60 seconds is the duration of 60 complete cycles, not a single cycle. B) 6 seconds is the duration of 360 complete cycles, not a single cycle. C) 1 second is the duration of 60 complete cycles, not a single cycle.